SW6C
CONVERSION OF ONGINIG SOLID NISIES INTO YEAST
... an economic evaluation
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This report
has been reproduced
exactly as received from the contractor.
No editorial or other changes
have been made,
although a new title-page and foreword have been added.
Figures related to solid waste generation and collection
are those of the author and based on information
available at the time the report
was written.
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CONVERSION OF ORGANIC SOLID WASTES
INTO YEAST
An Economic Evaluation
This report was prepared for the
Bureau of Solid Waste Management
by Floyd H. Meller
Research Division, IONICS, INCORPORATED
under Contrast No. PH 86-67-204
mvlromaental Protection Agency
Library, Region V
1 Horth Wacker Drive
Chicago, Illinois 60606
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Consumer Protection and Environmental Health Service
Environmental Control Administration
Bureau of Solid Waste Management
Rockville, Maryland
1969
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ENVIRONMENTAL PROTECTION AGEKCY
PUBLIC HEALTH SERVICE PUBLICATION NO. 1909
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402 - Price $1.76
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FOREWORD
This publication on the economic evaluation of the conversion of organic
wastes into edible protein will be of particular interest to readers in
universities and research-oriented organizations. The work was performed
under contract during the period 12 June 196? to 11 February 1968, and the
subsequent report is reproduced herein exactly as received from the con-
tractor, so that it can reach researchers as quickly as possible.
The present volume is another facet of the many demonstrable results
now forthcoming from passage of the 1965 Solid Waste Disposal Act, the
purpose of which was to initiate and accelerate research to better manage
the nation's solid wastes. This Act directs the Secretary of Health,
Education, and Welfare to carry out most responsibilities under the Act,
and the Bureau of Solid Waste Management was created for this purpose. Some
technical investigation and research are conducted by the Bureau in-house.
However, the vast research effort needed for learning how to manage the
nation's yearly volume of 3-5 billion tons of solid wastes requires intel-
lectual focus and cooperative studies from all possible quarters. Capa-
bilities of universities and other nonprofit organizations are being tapped
through research grants and other types of grants. Engineering applications
are being tested by institutions and communities across the nation through
demonstration grants. Grants to States for planning and to various smaller
regional groupings for study and investigation will lead to widespread
application of the results of this research and demonstration. The contract
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mechanism, which is resulting in reports such as this, has made it possible
to use the trained research staffs and accumulated practical experience of
commercial and professional consultants.
A nationwide effort is thus surging through the scientific and technical
community, gathering the substantive data, the fresh ideas, and the momentum
that will make possible the management of the steadily growing quantity of
sol id wastes.
--RICHARD D. VAUGHAN, Diveotof
Bureau of Sol-Id Waste Management
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CONTENTS PAGE
INTRODUCTION }
CONCLUSIONS AND RECOMMENDATIONS 4
A. Conclusions 4
B. Recommendations g
ECONOMIC CONSIDERATIONS OF SOLID WASTE RAW MATERIALS n
A. Urban Wastes 1i
B. Agricultural Wastes 2k
C. Wastepaper 27
D. Bagasse 31
E. Comments and Conclusions 33
THE HYDROLYSIS PROCESS 34
A. Introduction 34
B. Chemistry and Kinetics of the Process 34
C. The Batch Process 48
D. The Continuous Process 64
E^ Comments and Conclusions gr
THE FERMENTATION PROCESS 96
A. Introduction 96
B. Process Considerations 97
C. Economic Analysis 104
D. Comments and Conclusions 115
MARKET ANALYSIS FOR YEAST 116
A. The Protein Problem j]6
B. Current Market Situation for Yeast 533
C. Economics of Yeast from Wastes jl^c
D. A Brief Look into the Future j4g
REFERENCES ,51
APPENDIX 163
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LIST OF TABLES: PAGE
1 COMPOSITION OF HOUSEHOLD GARBAGE 12
II COMPOSITION AND ANALYSIS OF AN AVERAGE MUNICIPAL 15
REFUSE
III PHYSICAL BREAKDOWN - MUNICIPAL REFUSE 16
IV MONTHLY DISTRIBUTION BY WEIGHT OF ORGANIC AND INORGANIC 21
REFUSE DISPOSED OF IN NEW YORK CITY, 1939
V COSTS FOR SOLID WASTE DISPOSAL 22
VI FRUIT AND VEGETABLES: CANNING INDUSTRY DATA 25
VII WASTEPAPER PRICES - 1951 29
VIM WASTEPAPER SOLD BY WHOLESALERS BY URBAN AREA 30
IX COMPOSITION OF WOOD, PAPERS AND BAGASSE 31
X QUALITATIVE OUTLINE OF THE COMPOSITION OF WOOD 35
XI THE PERCENTAGE COMPOSITION OF CERTAIN WOODS 37
XII COMPOSITION OF THE TOTAL HYDROLYZATE OF WOOD 37
XIII YIELD OF POTENTIAL REDUCING SUGARS,AND FERMENTABLE 38
SUGARS FROM SAMPLES OF REPRESENTATIVE HARFWOODS AND
SOFTWOODS
XIV AVERAGE EQUIPMENT COSTS 55
XV ESTIMATE OF TOTAL CAPITAL INVESTMENT - BATCH PROCESS 56
XVI ESTIMATED MANUFACTURING COST - BATCH PROCESS 61
XVII AVERAGE EQUIPMENT COSTS FOR CONTINUOUS PROCESS USING 71
A FOUR-STAGE REACTOR SYSTEM
XVIII ESTIMATE OF TOTAL CAPITAL INVESTMENT FOR CONTINUOUS 72
PROCESS USING A FOUR-STAGE REACTOR SYSTEM
XIX ESTIMATED MANUFACTURING COST FOR CONTINUOUS PROCESS Jk
USING A FOUR-STAGE REACTOR SYSTEM
XX ESTIMATE OF TOTAL CAPITAL INVESTMENT FOR CONTINUOUS 76
PROCESS USING A THREE-STAGE REACTOR SYSTEM
XXI ESTIMATED MANUFACTURING COST FOR CONTINUOUS PROCESS 77
USING A THREE-STAGE REACTOR SYSTEM
XXII ESTIMATE OF TOTAL CAPITAL INVESTMENT FOR CONTINUOUS 82
PROCESS USING A TWO-STAGE REACTOR SYSTEM
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LIST OF TABLES (CONT1D)
PAGE
XXIII ESTIMATED MANUFACTURING COST FOR CONTINUOUS PROCESS 83
USING A TWO-STAGE REACTOR SYSTEM
XXIV FIXED CAPITAL INVESTMENT VS PLANT SIZE 86
XXV DAILY MANUFACTURING COST FOR CONTINUOUS PLANTS OF 88
VARIOUS CAPACITIES USING THREE-STAGE REACTOR
XXVI RAW MATERIAL FRACTION OF PRODUCT COST 89
XXVII PRODUCTION COST IN CENTS PER POUND OF SUGAR FOR 92
VARIOUS RAW WASTE COMMODITIES AND VARIOUS PLANT
CAPACITIES
XXVIII EQUIPMENT COST FOR FERMENTATION SYSTEM 107
XXIX ESTIMATE OF TOTAL CAPITAL INVESTMENT: FERMENTATION 108
PLANT
XXX ESTIMATED MANUFACTURING COST: FERMENTATION PROCESS 109
XXXI DAILY MANUFACTURING COST FOR YEAST AT VARIOUS PLANT 110
CAPACITIES
XXXII EQUIPMENT COSTS FOR FERMENTATION SYSTEM 111
XXXIII ESTIMATE OF TOTAL CAPITAL INVESTMENT: FERMENTATION 112
PLANT
XXXIV ESTIMATED MANUFACTURING COST: FERMENTATION PROCESS 113
XXXV DAILY MANUFACTURING COST FOR YEAST AT VARIOUS PLANT 114
CAPACITIES
XXXVI YEAST PRODUCT COSTS VS. PLANT SIZE 115
XXXVII PROTEIN SUPPLIES PER CAPITA BY MAJOR FOOD GROUPS AND 118
REGIONS
XXXVIII PER CAPITA PROTEIN SUPPLIES IN SELECTED COUNTRIES 119 & 120
XXXIX PROTEIN REQUIREMENTS AND SUPPLIES AVAILABLE 121
XL DISTRIBUTION OF WORLD'S POPULATION AND FOOD SUPPLIES 122
XL I AVERAGE YIELDS OF MAJOR CROPS AND CATTLE PRODUCTS 122
BY GROUPS OF REGIONS (1957-60)
XL 11 CURRENT CONSUMPTION LEVELS FOR INDIA, GROUP I 123
COUNTRIES GROUP II COUNTRIES, AND THE WORLD AS A WHOLE
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LIST OF TABLES (CONT'D) PAGE
XLIM AM I NO ACID COMPOSITION OF SOME SELECTED FOOD SOURCES 125
XLIV ESSENTIAL AMINO ACID CONTENT OF YEAST AND OTHER 126
PROTEINS (mg/gN)
XLV ESSENTIAL AMINO ACID CONTENT OF THE SINGLE CELL 126
PROTEINS
XLVI VITAMIN CONTENT OF SOME SELECTED MEAT CUTS (RAW) 127
XLVII WORLD PROTEIN PRODUCTION POTENTIAL (1962/63) BASED 132
ON CONVERSION OF CARBOHYDRATE OF SEVEN CROP PLANTS TO
PROTEIN USING FUNGI AS AGENTS OF BIOSYNTHESIS
XLVIM ESSENTIAL AMINO ACIDS 133
XLIX U.S. YEAST PRODUCTION 136
L UNITED STATES YEAST OUTPUT, 1963 137
LI WORLD YEAST PRODUCTION 137
LN CARBOHYDRATE MATERIALS USED FOR YEAST FERMENTATIONS 137
LI I I PRODUCTION OF INCAPARINA IN LATIN AMERICA 138
LIV ALTERNATE PROTEIN SUPPLY SOURCES iM*
LV COST SUMMARY ON SUGAR FROM ORGANIC WASTE HYDROLYSIS 146
LVI SUMMARY-YEAST COSTS VS ALTERNATE ANIMAL -EED3 148
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LIST OF FIGURES: PAGE
! TOTAL REFUSE PRODUCTION IN THE U.S. 20
2 PER CAPITA REFUSE PRODUCTION 20
3 WASTEPAPER PRICE TREND 1953-196? 28
4 COMPARATIVE RATES OF HYDROLYSIS OF VARIOUS SPECIES 40
OF WOOD
5 HYDROLYSIS OF DOUGLAS FIR OF VARIOUS PARTICLE SIZES 41
6 HYDROLYSIS OF DOUGLAS FIR AT VARIOUS LIQUID-SOLID 41
RATIOS
7 HYDROLYSIS OF DOUGLAS FIR AT 170°C. 180° and 190° 42
8 DECOMPOSITION OF SUGARS AT 180°C. in 0.8% SULFURIC 44
ACID
9 DECOMPOSITION OF GLUCOSE IN DILUTE SULFURIC ACID AT 45
170°, 180°, and 190°C.
10 RELATION OF FIRST ORDER REACTION CONSTANT k to ACID 46
CONCENTRATION IN DECOMPOSITION OF GLUCOSE AT VARIOUS
TEMPERATURES
11 RELATION OF FIRST-ORDER REACTION CONSTANT k TO 47
TEMPERATURE IN DECOMPOSITION OF GLUCOSE WITH SULFURIC
ACID OF VARIOUS STRENGTHS
12 FLOW SHEET OF WOOD HYDROLYSIS PLANT USING 50 TONS OF 50
DRY-WOOD SUBSTANCE PER DAY
13 BATCH PROCESS - FLOW SHEET 51
14 CONTINUOUS PROCESS - FLOW SHEET 65
15 VAPOR PRESSURE VS TEMPERATURE - WATER 67
16 COST RANGE PER POUND OF SUGAR PRODUCED VS PLANT SIZE 91
17 FLOW SHEET - FERMENTATION PLANT 105
18 CONVERSION OF INGESTED FEED TO FOOD 130
19 TOTAL CONCENTRATES AND FEED GRAINS FED 140
20 PROJECTED CONSUMPTION OF HIGH PROTEIN ANIMAL FEEDS 141
21 TEN YEAR PRICE TREND AND RECENT VARIATION ]42
A-1 CITY FARM CONCEPT 166
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INTRODUCTION
GOLD FROM GARBAGE is the euphemism attributed to the goals of
current research efforts and investigations into the utilization of the
solid waste materials generated by our society. Conservative estimates
place the yearly solid waste load at more than 165 million tons. By
1980, the burden will increase to an estimated 260 million tons per year.
The useful application of this current national liability will result in
a raw material asset from which viable industries of the future must evolve.
The adage of Waste Not, Want Not applies here. The conservation of
raw materials through reuse has been applied in the solid waste field
in the past. This has been particularly apparent during periods of national
strife when raw materials are in short supply. A case in point was the
increased utilization of paper wastes during World War II. During normal
economic periods however, the laws of the market place are king in a
free economy and technically useful materials are relegated to the waste
bin for economic reasons.
The assigned purpose of this study, therefore, is the economic evaluation
of one approach to the utilization of urban and agricultural organic
wastes. The direction of the study has been to investigate the economic
feasibility of converting urban and agricultural solid wastes to edible
protein. The approach to conversion of organic wastes to edible protein
utilizes a two stage process of hydrolysis and fermentation. The operation
and economics of each stage is examined in order in the text.
Wastepaper and bagasse were selected for specific study based on the
availability of economic data and the feasibility of a central supply
for these waste commodities. Wastepaper has the secondary advantage of
having been on the waste commodity market for a significant period of
time so that fluctuations of supply and demand on price can be evaluated.
It should be kept in mind that this selection of materials was made as a
convenience for economic evaluation and does not imply a limitation of
the process to these raw materials. In the case of urban wastes, the
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processing of mixed paper and organic garbage is felt to be feasible
and reasonable and is in fact considered as a third major raw material
source in this report.
The design of the hydrolysis process is based on work carried out
at the Forest Products Laboratory in Madison, Wisconsin. Saeman and
co-workers developed the necessary kinetic data for the hydrolysis of
wood. This information while not specifically applicable to wastepaper
and bagasse should give a conservative estimate of process economics
due to a slower rate of wood chip permeation by the hydrolyzing acid as
compared to pulped fibers.
Fermentation processing follows the traditional lines of the required
aerobic process for the propagation of cells. Special considerations
of plant location economics are evaluated and discussed.
Marketing considerations are based on the production of protein of
the general character of Torula Yeast (Candida utilis). Although
other single cell protein may actually be employed in the process due
to economic considerations such as propagation rate, the use of Torula
Yeast as a product choice gives a framework for market analysis based on
established nutritional values of a material that is capable of propagating
in the mixed sugars supplied to the fermentor from the hydrolysis plant.
The potential markets for protein supplements in the human food and
animal feed areas are considered in light of the present technology and
of current market trends. Marketing problems and competitive or alternate
product approaches are evaluated on a domestic and international basis.
No consideration is given in this report to the possible valuable by-
products that can emerge from the processing steps utilized. The exact
nature and quantity of by-product materials can only be derived from a
laboratory study of the processes using the actual waste materials being
considered. Process maximization for by-products of significant value
will of course, alter the overall economic picture.
It is not surprising that many assumptions had to be made in developing
this study. Qualifications and documentation have been included as
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justification insofar as is possible. Unfortunately, marketing projection
for the primary protein product is beclouded at this time by much opinion
and conflicting data.
Acknowled gemen t s
Grateful recognition is given to Professors Richard |. Mateles and Daniel
l.C. Wang, Department of Nutrition and Food Science, Massachusetts Institute
of Technology for their contribution to the fermentation section of this
report as well as their help in obtaining meaningful information on
yeast and protein markets.
Special recognition is accorded Kenneth J. McNulty of Ionics
Research Department who is responsible for the work on hydrolysis including
the addendum report to this volume.
Special thanks are given to the many individuals in industry,
government agencies and academic institutions who have contributed to
this story.
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CONCLUSIONS AND RECOMMENDATIONS
THE FOLLOWING CONCLUSIONS and recommendations summarize the problems
and prospects discovered in pursuing the goals of this study. Much work
lies ahead before the economic utilization of the wastes of our society
become a reality.
A. Conclusions
Economics of Waste Materials:
The economic consideration of solid waste raw materials is a complex
subject. Although wastes can be categorized into two main subdivisions
of urban and agricultural residues, this is insufficient for a quantitative
look at the raw material economics.
Problems involved in the definition of economics for urban wastes
include the composition of the refuse, the manner in which collection
affects refuse composition, the volume of refuse and the geographical and
population factors that affect both composition and volume. Studies to
date indicate that each municipality has unique characteristics and problems
in waste generation and collection. This would imply that processes
utilizing solid urban wastes as a raw material must be evaluated for the source
of supply on a local basis. In order to accomplish this task methods must
be developed to accumulate "standard engineering data" on municipal solid
wastes. Sampling and analytical techniques, while under current development,
require much improvement. The development of this data is bound to be
expensive since refuse composition is seasonal in nature requiring year
long studies to produce meaningful data. Perhaps predictable ranges of
refuse compositions will develop on regional geographic areas with qualifying
inputs for degree of affluence, etc. as more local studies are completed.
In any event the need for a "standard method" of sampling and analyzing
solid urban wastes is paramount.
When evaluating the economics of urban solid wastes it is impossible
to ignore the tremendous cost involved in collecting and transporting this
refuse to the disposal site. Although not directly associated, it is
desirable for new waste utilization schemes to have the latitude to accept
wastes that are transported to the plant site by means other than motor
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truck. Possibilities include pneumatic or hydraulic transmission, both
of which appear to be technically feasible.
The proposal of a utilization system for disposing of waste materials
ultimately brings the confrontation with current methods of disposal and
their economics. In the case of this study the use of urban wastes as a
feed to the hydrolysis-fermentation process must consider and condense
the myriad possibilities of raw material costs and credits that can be
concieved. Municipal dumping fees as currently used in compost plant
evaluations appear to be a realistic starting point. These plant credits
however must be tempered with raw waste preparation costs and possible
salvage markets. In this study two values were used for urban refuse:
One designated as "Organic Urban Refuse" applied dumping fee credits,
considering waste preparation costs to equal salvage values obtained on
segregation of organic wastes from cans and bottles, etc. at the source;
the second category designated "Mixed Urban Refuse" included an economic
penalty for the preparation of mixed raw refuse before introduction to the
hydrolysis plant. These two categories should bracket the economic
situations that can exist in a real application and therefore represent a
total range for the utilization of urban wastes by the hydrolysis-fermentation
operation.
As another approach to the raw material economics the use of a
segregated waste such as wastepaper which appears as a product on the
secondary materials market was considered in detail. The use of the lower
grades of wastepaper can be economically feasible and present a more
uniform feed to the hydrolysis operation. However, the price of this
material is controlled by the business cycles of the pulp and paper industry
which has experienced some wide fluctuations in the past twenty years.
These price swings could be disastrous to the economics of products produced
by the hydrolysis-fermentation process if wastepaper were the sole raw
material source. Paper wastes, however are stable in storage and may be
utilized to balance seasonal feed availability cycles for primary urban
organic refuse utilization plants.
Agricultural wastes are self segregating with regard to their
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economic usefulness as a feed to utilization plants. One major group of
agricultural wastes available in very large quantities are the residues
left in the fields after harvest of the primary crop. This includes straw,
cornstalks and cobs and other plant wastes where field harvesting has become
highly mechanized. The cost to collect these residues preclude their use
as a raw material feed to hydrolysis plants in the United States at this
t ime.
A second major group of agricultural wastes are the solid residues
collected at canning plants. These wastes have the advantage of being
available at a central location and at a probable negative cost to the
utilization process. Their production however, is limited to a very short
season. This coupled with a high perishability factor requires immediate
treatment of the wastes and hence a large facility representing a large
capital investment for the yearly (3 month/year operation)product ion of
hydrolyzate sugars.
One agricultural waste seems to combine the best features of the two
categories discussed. Bagasse, or sugar mill residues, is available in
very large quantities, is collected at a central location and can be stored
with minimum decomposition for periods of one year, it is currently used
as a fuel in the sugar mill and economic evaluations are based on fuel
value considerations of bagasse. The cost evaluation shows bagasse at the
sugar central to compete favorably with the current market alternate for
fermentation sugar, molasses.
Of the raw waste materials considered in this study as a feed to the
hydrolysis plant, urban organic waste shows the best economic promise.
Hydrolysis:
The hydrolysis process kinetics and hence the plant designs are
based on data assembled in the late 19^0's at the Forest Products
Laboratory in Madison, Wisconsin. This work represented a substantial
improvement in the German weak acid or Scholler process for the hydrolysis
of wood. It is believed that the use of wood hydrolysis data for the
development of hydrolysis plant costs will result in a conservative economic
estimate due to the physical differences of wood chips and pulped fibers.
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Reaction rates may be significantly higher for the pulped fibers resulting
in higher sugar production rates or smaller plant size with the parallel
reduction in product costs.
it is apparent from process parameters that a stagewise continuous
process will result in minimum loss of sugar due to secondary degradation
and hence is the most desirable process. Calculations show that a three
stage continuous reactor represents the optimum economic condition, with
low hydrolysis acid concentration and maximized temperatures being preferred
operating conditions. As is normally expected with processes of this type
product costs decrease with increasing plant size.
Valuable by-product credits were not considered in the economic
evaluation and represent a valid source for additional process revenues.
Conclusions on this aspect cannot be made until laboratory studies of the
process using the selected waste feed are conducted.
Fermentation:
The fermentation plant was designed on traditional proven standards.
The application of new technologies could have a significant influence on
the product cost from this operation. The fermentation step as presented
in this study represents the larger fraction of the final product cost.
Several items can be considered in attempting to reduce costs of the
fermentation step. Two discussed in the report are the material of
construction of the fermentor and the method of cooling used. In the
case of fermentor construction significant savings can be realized by
making this vessel of coated wood. Concrete construction may also be a
favorable alternate. Cooling costs, however, represent a prime cost
reduction area for special geographic situations. The availability of
large bodies of surface cooling water such as sea coast locations can have
a profound effect on product costs when this cooling water source is used
in place of refrigeration-cooling tower systems.
Recycling of process water from the fermentation plant to the hydrolysis
plant and operation of the fermentors at lower pH levels than considered
in the hydrolysis plant calculations can result in overall process economies
that are worthwhile. These logical considerations should insure conservative
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economic figures for this process phase.
The choice of organism for the fermentation plant is an important
consideration. Candida utllis was chosen for the study because process
information and marketing data are available for this species. The fact
that this material has been marketed also results in a wealth of preliminary
knowledge of the organism with respect to its value as a food and animal
feed source. Other microorganisms may be selected for laboratory studies
that have special value to the economics of a process such as the hydrolysis-
fermentation complex. For example, species with higher reproduction rates
can reduce fermentor size, thermophilic organisms may operate at temperatures
that reduce the high cost cooling problem, or perhaps species can be
developed that will reproduce directly in the acid hydrolyzate liquors
eliminating the neutralization step. These factors must be considered in
detail in a laboratory study. If successful, animal feeding studies using
protein from the new organism must be made before a material of marketable
status evolves. It is significant to note however, that most early work
on wood hydrolyzate fermentation for the production of yeast employed the
Candida utilis species, popularly called Torula yeast.
Market Analysis:
The product of the hydrolysis-fermentation plant as conceived here
is Torula yeast. This material is useful as a protein supplement in
human food or a vitamin and protein supplement in animal feeds. Although
many minor markets exist for this commodity such as pharmacuetical
applications, food flavors, etc. the bulk markets are the food and feed
supplements.
Much work has been done by various national, industrial and international
groups to quantify the world protein needs and find acceptable solutions to
this ever increasing problem. The availability and possible limits of
expansion of traditional protein sources, meat, milk, eggs, fish, grains,
pulses, etc. indicate needs by the year 2000 beyond the capability to
produce. Then too, some of the traditional protein sources are deficient
in some essential amino acids such as lysine, etc. requiring supplementation.
The general concensus is that new protein sources will be needed and
welcomed in the market place if they can be produced as economical and
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acceptable foods. Various market contenders under development include
fish protein concentrates, oilseed meals, yeasts, algae, fungi and bacteria.
Chemical supplementation of amino acids is finding favor in some current
applications. On a long term basis, a food market seems to be available
to all competitive sources of protein.
Today, however, and probably in the long term also the marketing of
"new" foods seems to be a monumental task. Several factors contribute to
the problem of which the fact that the largest market need is in countries
that are least able to pay is not the least significant. Where economies
are strong the preference for animal protein is always in evidence. This
seems to indicate, along with other factors, that the animal feed market
is the probable goal for any new large volume protein supplement products.
Current high protein supplements for animal feed include soybean
meal, cottonseed meal, and animal and fishmeal products. Calculated costs
for Torula yeast from hydrolyzed solid wastes are at best at the high end
of the current high protein supplement price range based on the cost
figures developed in this report. These costs for Torula yeast however,
are less than half of the present price cited for the same product from
sulfite waste liquor. Sulfite waste liquor yeasts are in current use as
high protein supplement for animal feeds in special situations in the United
States and on a more common basis in Europe.
Serious penetration of the high protein animal feed supplement market
in the United States by yeast from hydrolyzed solid wastes is a function
of process improvements evolving from laboratory studies of a combined
hydrolysis-fermentation operation.
B. Recommendations
Results of this general economic study have been encouraging as to
the prospects of a hydrolysis-fermentation approach to the disposal of
certain organic wastes. While certainly not a panacea, the application
of this technology to the utilization of urban organic refuse appears
quite promising.
As is pointed out in the text the costs for the hydrolysis process
were developed from the kinetics of a similar but different feed material.
Valuable data on by-product production and processing problems cannot be
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anticipated in this way and therefore directs future work to evaluations
of the process using wastes of the presumed composition and physical
nature to be employed in a working system. A laboratory and pilot plant
study on the hydrolysis of organic urban wastes is indicated here.
If organic urban wastes are to be considered in the laboratory
evaluation of hydrolysis, a more basic problem must be considered. That
is, what is the composition, or more nearly, what is the composition
range of organic urban wastes? Studies of this factor are under way,
but published meaningful data will be necessary to aid the investigator
in utilization process development. Continued support and emphasis on
these study programs is strongly recommended.
The influence of "tramp" substances such as plastic wrapping material
and aluminum foil on the hydrolysis process must be investigated and should,
of course, be included in any laboratory study on this process. However,
the manner in which these materials affect the fermentation operation must
also be determined. Fermentation rate studies based on various hydrolyzates
and impurities therein from organic urban wastes represents a third important
area for recommended study. This phase should include animal feeding
studies.
The development of continuous culture techniques and the fermentation
process optimization have a strong influence on the overall process
economics. A detailed study on a laboratory and pilot plant basis is
needed to define the working system.
The culmination of the laboratory and pilot plant studies suggested
will be a definitive cost study of the process. At this point it appears
that the combined hydrolysis-fermentation process for the production of
yeast has the potential to become a factor in the future economy. An
actual study is needed to determine if in fact a viable industry can grow
on urban refuse.
10
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ECONOMIC CONSIDERATIONS OF SOLID WASTE RAW MATERIAL
A. Urban Wastes
THE NATION SPENDS three billion dollars annually 1>2'P132 tQ dispose
of garbage and refuse. Total urban waste loads for the U.S. have been
reported by investigators at 152 to 1&7 million tons per year. '
Indirect costs and economic losses due to poor waste handling add another
measure to the mounting bill. I terns such as environmental pollution,
depreciated property values, fire and rodent damage and attendant medical
bills are included in these hidden costs. And yet, these costs may
actually be a small fraction of the total which is represented by the
current preoccupation of "wasting" the vital resources that are represented
in the heterogeneous mixture termed rubbish. It is time to dedicate
engineering and scientific endeavors to the reclamation and utilization
of these so-called waste materials.
Composi tion:
Knowledge of the physical and chemical composition of municipal
wastes is surprisingly small. Work to define the composition of refuse
has only been conducted over the last decade with the initial work in
this area being conducted in Western Europe by the International Research
Group on Refuse Disposal.
While the work in Western Europe is of academic interest here, it
will not define the municipal waste compositions in the United States.
Table I indicates the variation of waste composition on a location basis.
Waste composition information for Germany, for example, would not apply
to the California situation. Therefore, waste utilization plant designs
must be based on realistic current local data.
The value of current waste composition information is pointed up by
studies ^P-2^'2^ |n New York and Chicago in 1939 and 1956 through 1958
respectively. The Chicago data showed garbage contents of 28 percent
and ash kk percent of New Yorks 1939 study while the paper content
increased to 250 percent of the earlier figures. Changes in food processing,
fuels and packaging are no doubt responsible for these variations along
11
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with the Increased affluence of the nation. It is not only desirable,
but necessary, to develop waste composition measuring tools so that
meaningful data can be made available to waste utilization plant design
engineers.
Rogus ' states that "The development of measuring, sampling, and
laboratory technqiues to a common accepted standard is a laborious,
costly proposition, requiring a uniform approach to a non-uniform material".
He goes on to list the factors that affect the characteristics of
4 p jQ-20
municipal wastes as follows :
1. Number and types of industries and degree to which their wastes
are self-disposed.
2. Number and types of commercial establishments and degree to
which their wastes are self-disposed.
3. Climate to illustrate: in the warm belt the output of ashes
will be negligible, whereas the amounts of garden trash may be
abnormally hi gh.
4. Seasons -- the winter and holiday months will probably produce
higher amounts of textiles and wrappings but less of fresh
vegetable and fruit wastes.
5. Income level residential areas in the high income brackets
acquire and waste more per capita.
6. Population density the high density apartment house areas will
generally put out all the wastes they produce (unless they are
equipped with on-site incinerators) while the individual homeowner
will tend to dispose of some of his wastes. Conversely, the
apartment house districts will put out fewer leaves, tree clippings,
and garden wastes.
7. Technological advances developments in food processing such as
pretrimming of fresh vegetables, quick-freezing of many types
of foods, canning of fruit concentrates, etc., have all contributed
to reducing the garbage content to about 1/3 of its previous value -
all within one generation. The ever increasing use of non-solid
fuels has almost eliminated the former high ash content. The
development of many types of synthetic wrappings and the new
13
-------
systems of pre-packaging of many marketable items have increased
the amounts of paper, cartons, and many varieties of synthetic
tissue, to a degree where they have more than made up for the
reductions in food waste and ashes.
8. Degree of self-disposal -- on-site incineration and garbage
grinding does, where used, have a sizeable effect on the amount
and character of wastes.
9. Frequency of collection where collection schedules are
generous the output is untrammeled. Skimpier schedules tend to
restrain the average output.
10. Fees a charge for collection services, usually in direct
proportion to the amount of material put out, will invariably
reduce the degree of wastage and encourage some self-disposal.
11. Salvaging an attractive market for such salvables as paper,
rags, metals, or bottles will induce many householders or janitors
to cull out these materials from the waste put out for collection.
12. Cost and availability of fuels when the cost of fuels for
cooking and/or heating is high and they are difficult to procure,
the tendency is to utilize some of the combustible refuse for
these purposes either in the cooking range, in the furnace, or
in the fireplace.
With this wide variety of factors affecting the composition of
municipal wastes it becomes apparent that the development of a "standard
method" of sampling and analyzing refuse must be established. Work on
this problem was discussed by Professor John Bell in his paper presented
at the National Conference on Solid Waste Research in December, 1963. The
ultimate value of this study is the development of engineering data for
specific municipalities of the type assembled by Mr. Elmer Kaiser
from Professor Bell's results as shown in Table II. Many studies have
been performed on municipal waste compositions and are reported in the
literature. 'P '°'9' A summary of nine studies carried out by USPHS,
APWA and university personnel is contained in the data in Table III.
-------
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-------
Type
Paper
Leaves
Wood
Synthetic
Cloth
Combust ibl es
Garbage
Glass
Metal
Ashes, stone, dust, etc.
Non-combust ibl es
Percent of Total
Wet
^8.0
9.0
2.0
2.0
1.0
62.0
16.0
6.0
8.0
8.0
22.0
by Weight
Dry
35.0
5.0
1.5
2.0
0.5
M*.0
8.0
6.0
8.0
6.0
20.0
Total moisture content
28.0
16
-------
The tabulation offered by Mr. Kaiser will be very useful to
engineering studies on waste utilization. The fact that an average
municipal refuse contains 46.63 percent cellulose, sugar and starch
on a dry basis makes it a useful raw material commodity for a hydrolysis-
fermentation plant. However, the actual supply of this carbohydrate
fraction considering seasonal variation will be the design parameter of
ultimate importance.
Collection Methods:
The method used in collecting and transporting the waste commodity
to a treatment plant will have a significant influence on the overall
economics of the waste disposal-utilization complex. The location of
plant sites and waste segregation methods are important ancillary
considerations attached to the collection scheme.
Reports ' ' dealing with refuse collection and disposal
show collection costs to be an extremely large component of the total.
Where incineration is used as the disposal means, collection costs represent
60 to 70 percent of the total bill. In the case of landfill operations
80 to 95 percent of the cost is in collection 'and transportation. Data
for municipal disposal for the city of Philadelphia show collection costs
. ., 2,p249
at nine dollars per ton.
With the collection factor in mind it is simple to agree that solid
wastes delivered to a treatment plant site do have a value. The value
added to refuse by virtue of its collection may then, on an extremely
conservative basis, represent the raw material cost to a waste utilization
plant. The actual assignment of this cost by a municipality to a processor
seems unrealistic, however, since the alternatives are rather unappealing.
1 C*. *) £.
Current practice for converting refuse to compost indicates the
willingness of municipalities to assign negative values to refuse in the
form of a "dumping fee" paid to the treatment plant.
The important point to consider is the fact that the collection costs
are an integral part of all refuse utilization systems and should not be
excluded from the economics. If this point is accepted, the design of the
17
-------
collection method becomes an important factor in system economics.
Bowerman stated ."Most solid waste transportation systems utilize
automotive vehicles exclusively; it is safe to say that the one major change
in solid waste collection in the last 100 years has been the conversion from
horse-drawn wagons to gasoline-powered trucks. ... but some glimmer of hope
lies in the present day usage of garbage disposers ... our present technology
suggests that grinding at each individual home may not be practical ... It
does appear that some merit exists in grinding rubbish to the sewers at trans-
fer stations where the solid waste unsuited for carriage in the sewer (cans,
bottles, tree limbs, etc.) would be hauled away for disposal elsewhere. With
such a system, the sewer serves as an "endless belt" type of conveyor to de-
liver the ground refuse at nominal cost to sewage treatment plants ...
The feasibility of transporting organic refuse by grinding to a trunk
sewer was demonstrated by Bowerman in Los Angeles where 7 tons of refuse was
ground (particle size 3 to k inches) to the sewer In 30 minutes with no apparent
transport problems.
Systems of the type envisioned by Bowerman would reduce refuse hauls to
a neighborhood basis with some extended runs to landfills for disposal of the
can and bottle fraction separated at the transfer station.
An interesting concept of a neighborhood waste collection system has been
employed for 5 years in a hospital at Solleftea, Sweden and is currently being
installed at a housing estate at Sandeberg to service an estimated 2,770 family
1*4
units. Refuse is transported by a pneumatic system to a central collection
silo from which the waste is transferred to the ultimate disposal system
(on-site incinerators in Sweden). The system as described by Mr. Merchant is
"the most advanced method of refuse conveyance so far achieved".
It does appear from the foregoing examples that the collection of wastes
need no longer be consigned to the gasoline powered wagons that have so long
served as the only practical means of transporting refuse. Design alternatives
may now be considered with "total system" economics serving as a basis for
selection.
Volume:
When considering waste as a raw material or feedstock commodity for a
continuous processing plant, the reliability of supply becomes an important
factor. It is logical to size a facility on the average quantities available
18
-------
in any yearly cycle of the waste to be used» Storage capabilities can balance
short term volume variations and refuse production projections must, of course,
be considered for overall plant growth needs.
Projected refuse production volumes are shown in Figures 1 and 2. The
monthly variation in refuse composition for New York City in 1939 is shown in
Table IV. Although the latter reference does not represent refuse compositions
based on typical wastes of today, the point of seasonal variation in composi-
tion is well illustrated. Monthly tonnage volumes over a similar time period
vary only fifteen percent. The refuse production in the U. S. is
o n 1 ft?
currently increasing at a rate of 2 percent per capita per year. >p This
coupled with a 2 percent annual population increase results in an overall
refuse production increase of k percent per year.
The availability of a large and increasing supply of refuse in the U.S.
appears to be assured. The availability of individual constituents in the
waste, however, must be analyzed on a whole year basis for each location
cons idered.
Preparation Requirements:
The condition of the delivered waste, the economics of the local salvage
market and the utilization process requirements all affect the degree of
treatment the raw waste is given prior to processing. In general, bulky
refuse such as cars, refrigerators, etc. would not be accepted at a utiliza-
tion plant.
When truck transport of wastes is used, the method of removal of re-
fractory components will be based on the economics of the local salvage
9 17
market. If economically desirable, a picking belt would normally be
installed for salvage operations. If salvage is uneconomic other techniques,
used by composters, ' ' waste paper processors ''P* and in some cases
mining operators, may be employed. They include:
19
-------
1920^930\SkQF950f96~6f§701
Year
FIGURE 1. TOTAL REFUSE PRODUCTION IN THE U.S.
2,p.133,15
-------
TABLE IV:
MONTHLY DISTRIBUTION BY WEIGHT OF ORGANIC AND INORGANIC REFUSE
DISPOSED OF IN NEW YORK CITY.
Month
January
February
March
April
May
June
July
August
September
October
November
December
Per Cent by Weight
Organic
Garbage Misc. Paoer Wood Total Metal
5.7
9.0
9.7
18.1
26.7
35.1
43.8
23.1
12.6
10. 1
6.6
3.5
1.0
1.7
2.1
2.8
3.3
3.8
4.1
7.4
5.6
3.8
1.9
0.8
12.4
12.6
20.6
21.6
23.0
24.3
25.5
37.6
26.7
31.0
18.0
9.0
0.3
0.7
0.3
2.0
3.1
4.6
5.9
3.8
4.9
2.6
2.1
0.8
19.4
24.0
32.7
44.5
56.1
67.8
79.3
71.9
49.8
47.5
28.6
14.1
4.3
6.6
7.4
7.4
7.1
6.4
6.6
11.6
8.2
8.9
3.8
3.1
1 norganic
Glass Ashes
4.0
4.9
7.3
6.9
6.8
6.8
6.3
5.1
9.1
4.0
2.9
1.9
72.3
64.5
52.6
41.2
30.0
19.0
7.8
11.4
32.9
39.6
64.7
80.9
Total
80.6
76.0
67.3
55.5
43.9
32.2
20.7
28.1
50.2
52.5
71.4
85.9
Average
17.0
3.2
21.9 2.6 44.7 6.8
43.0 55.3
21
-------
Grinding or Rasping
Magnetic separating
Hydrapulpi ng
or using, Gravitational separators
Ballistic separators
Hammer Mills
Although salvage of metal components is possible using these techniques,
paper and salvageable bottle values are certainly lost.
If waste is segregated at the source, homes, commercial establishments,
etc. virtually no separation problems need exist at the utilization plant and
only valuable salvage operations would be considered. This general comment
would also apply to the unique system where wastes are segregated prior to
grinding and transmission by sewer line or other pipe line systems.
In overall process economics, the trade-off between in plant preparation
vs: collection method costs will be the factor to consider.
Current Disposal Methods:
The dollar value of solid waste raw materials as a feed commodity in a
utilization plant must of course be considered in context with competing
process uses or disposal methods.
At the present time the large volume of wastes produced by the U. S. pop-
ulation have no positive market value. In reality they are a municipa 1 liability
that can be directly measured in part by current disposal costs. Typicaili costs
are summarized below:
2,pig6
TABLE V: Costs for Solid Waste Disposal K
Cdpital Cost
(land excluded) Operating Cost
Dollars per ton per day Dollars per ton disposed
Sanitary Landfi 1 1 1000-2000 $1.25-2.25
Central Incineration 3500-7000 3.50-5-00
Composting 1500-10,000 2.00-7-00
Maintenance and operation of open dumps is estimated at 5 to 25 cents
per ton.^1
22
-------
The use of the sanitary landfill procedure for organic refuse, while
the least expensive of t!ie acceptable alternatives presented, appears
to present a problem to municipalities when new locations are required.
Public acceptance of landfills is difficult due to the wrongs and abuses
of open dumps. When sites are found, they are generally at an undesirable
distance from the city resulting in increased hauling costs.
Incineration is finding increased favor in spite of the relatively
adverse economics. Incineration techniques, while improving, are a
20
cause for concern by air pollution agencies. Acceptable stack effluents
will require additional capital investment and operating expenses resulting
in increased process costs. Present day cost figures should be minimum
values.
Composting, while having the right philosophical basis, has not
become popular in the U.S. to this time. The delay in the establish-
ment of salvage and product markets has hindered progress and has
resulted in the requirement of basing plant economics on a numicipal
dumping fee only. ' The fact that this is an acceptable basis to
22
some municipalities is demonstrated by the City of Houston's commit-
1 "7 O £.
ment " to pay $3.^7 per ton of refuse delivered to the Houston
Compost Plant.
It must be concluded from the above that mixed refuse from municipalities
has a negative asset value. Based on the Houston example, it is logical
to assume that this value will approach the cost of incineration. Jo'tn R.
21
Snell states that "If salvage and compost sales are neglected, the
Tcompositingl plant can be maintained, operated and amortized for a
dumping fee of approximately fifty cents to a dollar less than a com-
parable sized incinerator ...".
Using this range and the incineration of operating costs noted in Table V,
the dollar liability of mixed refuse for municipalities can be conservatively
established in the 2.50 to k.SO dollars per ton range. This "dumping fee"
23
-------
should be collectable by any process utilizing municipal wastes.
B. Agricultural Wastes
There are two broad groups of organic agricultural wastes that require
better disposal systems. They are: animal wastes and plant wastes.
The first category described by Taiganides ''as the "more vexing"
will not be discussed here since our major concern is with cellulosic
waste materials. The second category, plant wastes, can also be subdivided
into two groups; canning wastes and crop residues.
Utilization of the wastes generated by the fruit and vegetable
canning industry, and the fraction of feed and grain crops remaining as
residues has challenged the abilities of many researchers in public and
private endeavors for many years. A variety of successful products have
evolv&d from these efforts, but their effect on reducing the tremendous
volume of wastes available annually from agricultural sources has been
minimal. The following discussion summarizes the problems and some of
the utilization efforts reported to date. No attempt has been made here
to be complete since the volume of work done in this field is large and
varied.
Canning Wastes:
The volume of canning wastes in California's Central Valley was
discussed by Mr. Walter Mercer, >P at the National Conference in Solid Waste
Research in December, 1963. He stated: "Each year 700,000 to 800,000
tons of tree fruits are grown in California's Central Valley ...
Between 12 and 1^ percent of this raw tonnage becomes a waste material
consisting of pits, peels, green fruit, and defective pieces not suitable
for canning.
Of the 3,150,000 tons of tomatoes .... 7 to 10 percent of the
tonnage must be handled as waste product. ... All together, it is
estimated that each year during the three to four months of canning,
between 500,000 and 600,000 tons of wet wastes are produced and must be
disposed of by some method."
Volumes of produce and their associated waste loads are available
oq 26 27 29
in the literature. ' ' ' ? Table VI is one example.
-------
TABLE VI: FRUIT AND
Product
Average Season (weeks)
Tons Raw Material Rec'd:
Per Plant-Avg. Year
Per Plant-Max. Day
Tons Solid Waste Produced:
Per Plant-Avg. Year
Per Plant-Max. Day
Avg. Tons Waste/Raw Ton
Apples
13
3137
46
1462
19
0.47
VEGETABLES: CANNING INDUSTRY DATA
Berries
6
845
47
45
4
0.05
Peaches
k
1249
85
132
20
0.11
Pears
8
6059
139
2765
55
0.46
Asparagus
6
859
35
260
12
0.30
Beets
8
4772
126
1831
42
0.38
Corn
6
5349
253
3845
178
0.72
Peas
6
5108
213
389
16
0.08
The problems associated with the utilization of the wastes generated
25 28 29
at canning plants have been tabulated and repeated by many, ' ' The
difficulties include the following:
Seasonal nature of the wastes
Perishable nature of the wastes
Pesticide residues in the wastes
Added responsibility for food processors at their
busiest time
Minimal economic return on waste oriented by-
products
Although these problems are real, the alternative difficulties of
disposal of these wastes is always increasing and of tremendous
24
magnitude. Therefore, a continuing economic pressure will be exerted on
the canneries to find ways of using waste commodities in an efficient manner.
Utilization efforts have centered largely around animal feed applica-
tions in the past with wet waste feeding, dried waste feeding and storage
2L{ 28 30
and mixed waste ensilage experiments being of major* interest. '
The current use of pesticides which are concentrated in fruit and vegetable
skins reduces the desirability of using those wastes as animal feeds.
California canners are jointly financing a utilization scheme that
converts peach pits to charcoal briquets. '" This process appears
to have economic promise.
Other developments include the use of pits as a metal cleaning medium
used by blasting techniques and the conversion of pear wastes to alcohol
28
by fermentation. The latter case was a short run success which was
eventually abandoned.
25
-------
The short season and large volume of perishable material makes
utilization of canning wastes an extremely difficult and challenging
problem.
Crop Residues:
Utilization of crop residues has been traced to 1?0 BC when the
Romans were separating starch from a type of corn. Residues for the
purpose of this discussion include cornstalks and cobs, straws, stems,
bagasse, hulls, and other woody wastes not generally associated with
canning type operations.
The U.S. Dept. of Agriculture estimated a 200 million ton per
year production of this type waste of which less than one percent is
used.
The large bulk of the crop residues are left in the field at the
time of harvest. With the advent of combine harvesters, corn pickers
and shellers and other field processing equipment the era of the straw
pile is gone. The main problem and raw material cost for utilization of
most crop residue wastes is that of material collection and transportation.
Although it has been estimated that the annual amount of wasted straw is
sufficient to satisfy all of the annual U.S. cellulose demand, it is
not utilized for economic reasons.
Current applications of this classification of materials include
their use in the manufacture of:
building board (various types)
paper
soil conditioners
animal feeds
litter for poultry houses
furfural
a 1coho1
sugar solutions
yeast
packing materials
sweeping compounds
32
A selected bibliography covering "unconventional" uses for crop
residue waste materials has been published and includes more than 300
references dating from 19^+2.
26
-------
Where collection costs and long transportation hauls can be avoided,
crop residue wastes should find increasing use as process raw materials.
The fact that they can be stored for significant periods without gross
degradation allows continuous year long operation of a processing plant
thus putting capital investments on a continuous use basis.
C. Wastepaper
The purchase of organic waste raw material from an established
secondary materials commodity market for feed to the hydrolysis-fermenta-
tion system can be well illustrated by the wastepaper field. The
advantage in this approach is the segregation of raw material and hence
the relatively uniform feed composition presented to the treatment plant.
The disadvantage over mixed organic refuse is cost.
Paper waste is collected on a local basis by secondary materials
dealers for resale as paper stock to manufacturers of paperboard, insula-
tion board and, where sufficiently segregated for reuse, in higher grade
paper production. The Paper Stock Institute of America in their Circular
3^
PS-66 define k$ grades of paper for reuse.
The annual tonnage of all grades of paper stock consumed by industry
is in excess of ten million tons. Total production of all grades of
paper and paperboard exceeded four times this figure in 1966 at about
forty six and a half million tons. Normally, paper stock moves from
collector to consumer within a single metropolitan area with the normal
distance of transport not exceeding fifty miles.
A price history for the No. 1 mixed paper grade of wastepaper in the
Boston area is shown in Figure 3, with national area variations for six
grades for 195' displayed in Table VII.
27
-------
30-
o
(-
in
o
o
UJ
O
a:
a.
1953
1955
1957
1959
1961
1963
1965
196?
Year
FIGURE 3: WASTEPAPER PRICE TREND 1953-196736
NO. 1 MIXED GRADE
28
-------
TABLE VII: WASTEPAPER PRICES - 1951
(Dollar Range per Ton)
36,39
Hard white envelope
White ledger
Corrugated
Over issue news
No. 1 News
No. 1 mixed paper
New York
200/245
130/140
64/70
40/45
37/41
32/35
Phi ladelphia
225
125/130
55/62
4o
33 AO
32/35
Boston
200/235
125/140
40/61
33A5
28/31
29/32
Chicago
190
125
52
41
35
27
Paper stock experiences fluctuations in availability that is
certainly influenced by price. The higher the price, the greater the
incentive on collection agencies such as the Boy Scouts and church groups
to pick up wastepaper, particularly old news. Seasonal variations are
also experienced with the highest quantities available during Spring and
35
Fall house cleaning periods.
Availability of paper waste is a function of other factors too. The
type of municipal waste collection service and disposal means employed
in a community plus local laws on backyard incinerators can have a
marked effect on the total paper load collectable within a community.
Increases in waste collections of 35 to 100 per cent have been recorded
in controlled experiments where backyard burning was banned. '"
Table VIM shows the daily volume of paper stock sold by commercial
wholesalers in various metropolitan areas in the U.S. in 1963. Using
Rogus1 data '^ for New York City and applying the average municipal
paper percentage from Table III, we have an average waste load of
14,000 tons per day times 48 percent paper equals 6,700 tons per day of
paper actually disposed of by the populace but uncollected by the
wholesalers.
Coincidently this number for uncollected waste paper in New York
City just equals the amount of wastepaper collected by wholesalers in
the consolidated New York and Northeast New Jersey area. From this it
is possible to conclude that sufficient paper wastes are available in
this area to double the present wholesale collections. The effect of
increased demand on the price structure of the waste commodity is
impossible to estimate however since it is collection costs and market
-------
demands that will fix the price and not mere availability figures.
TABLE VIM: WASTEPAPER SOLD BY WHOLESALERS BY URBAN AREA38
New York & NE New Jersey Consolidated Area 6,700 Tons/Day
Chicago & NW Indiana Consolidated Area 3,800
Philadelphia 2,1*00
Boston 1,500
Detroit 1,150
Los Angeles & Long Beach 1,1^0
San Francisco & Oakland 820
Cleveland 725
St. Louis 500
Kansas City 325
Memphis 270
Dallas 230
Houston 180
At the present time the availability of new pulp for paper
manufacture has reached record highs while demand has not kept pace.
The effect on the waste paper market has been to reduce prices to the
historical low ranges with the result of increased closing of paper
stock wholesalers. Current outlooks for the wastepaper market look
dim. With pulp selling at $85 per ton, high grade wastes that traditionally
sold in the $125 per ton range must now reduce to the eighty dollar range
to compete.
It would appear reasonable that prices for wastepaper feed stock
based on a ten year range can be applied to a new waste utilization process.
The price range on this basis for No. 1 mixed paper is $** to 12 per ton.
The volumes available at these prices should be somewhat greater, say a
ten to twenty percent increase over the figures in Table VII, than the
current collection rate if a market were available. A significant increase
in collectable mixed paper should be experienced if air pollution laws
are instituted that forbid backyard burners.
30
-------
The price-demand relationship for wastepaper is tied to a large
degree to the productivity-demand cycle of pulp. As long as pulp
productivity remains high relative to demand, the demand and hence the
price for wastepaper will remain low.
Utilization of Wastepaper as Process Feed:
Paper waste as a feed for the hydrolysis-fermentation plant appears
to have desirable qualities for this study. Early work on the kinetics
40 41
of hydrolysis was conducted on wood chips. ' The rough analysis of
19
various types of paper and wood are shown in Table IX. The similarity
of the two materials allows the use of the kinetic data developed for
wood to be applied to paper wastes with some degree of confidence. It
is expected that the rate data for wood will be conservative when applied
to paper stock since permeation of the cellulose fibers by the hydrolyzing
acid should be more rapid and complete for the loose paper fibers than
the consolidated wood chips.
TABLE IX; COMPOSITION OF WOOD. PAPERS19AND BAGASSE**2'**3
Wood
Groundwood
Sulfite
Sulfate Paper
Baqasse
Cel lulose
Hemi Alpha
20-26% 44-50%
20-26% 44-50%
90%+
80% +
50-53%
Liqnin
1 7-30%
1 7-30%
2-5%
7-12%
1 1 -25%
Extractives
And Ash
3-8%
3-8%
Bal.
Bal.
Bal.
D. Bagasse
The utilization of crop residues has been discussed briefly in an
earlier section. The main economic problem anticipated is that of
collection of the waste material. In the case of bagasse this problem
does not exist.
Sugar cane is transported to a central processing plant where it
is crushed, sugars extracted and the remaining fibrous waste (bagasse)
stacked on a waste pile. The normal application of this waste is as
44
fuel for the processing plant. The material's poor fuel characteristics
31
-------
Indicate that this utilization technique is more nearly a waste disposal
method. Current trends in air pollution abatement indicate that this
use of bagasse will be undesirable.
The abundance of bagasse as a raw material has been estimated at
20 million tons annual world production with a U.S. total including Hawaii
I eL
and Puerto Rico at 9.6 million tons. Of more interest is the amount
available at a single location for processing. A typical mill will
produce 42,000 tons of bagasse per year while a high efficiency mill
will produce twice this figure.
Bagasse wastes have been used to make a variety of products
. , .. JL 45,47 lt 44,48 44,49 . . 47,51
including hardboard, ' cellotex, paper, ' plastics,
52
chemicals and charcoal. It has been utilized at the sugar central as
a fuel, spread on the land as a mulch and fertilizer and fed to live-
stock. In spite of the many applications there appears to be no problem
of avallabiIity.
A conservative estimate of raw material costs associated with
bagasse would be equivalent to its value as a fuel plus transportation
and handling costs.
42
Raw material costs on this basis were estimated as follows :
Raw material at sugar central (fuel value) 0.25 cents/pound
Baling for shipment 0.25
Transportation to processor (within 50 mile radius) - 0.25
Total Cost 0.75 cents/pound
Sugar mills generally operate on a 70 day grinding season. During
this period the 42 to 84 thousand tons of bagasse are generated and
stacked. The utilization of this waste, however, can be spread over a
longer operating period since techniques allowing storage for up to
42 44
twelve months have been developed that minimize deterioration problems. '
With the short primary product season of 70 days for a sugar mill,
it would seem logical that a waste utilization plant be installed at the
sugar central providing a second product. This would allow a year round
application of the labor force at the sugar central and a reduced cost of
secondary raw material due to the elimination of baling and transportation
costs for the bagasse. Other advantages may accrue from such a combined
operation by the utilization of liquid waste streams from the sugar
32
-------
operation in the fermentation process.
Preparation of the bagasse raw material for a hydrolysis operation
should be minimal and result largely in a materials handling operation.
E. Comments and Conclusions
Three major sources of wastes have been explored as potential raw
materials for a combined hydrolysis-fermentation process. The availa-
bility, or rather, over abundance of mixed municipal organic wastes and
bagasse make them logical candidates for processing. The use of waste-
paper, while desirable from a predictable composition basis, may be a
less suitable material due to fluctuating price and availability.
Urban waste utilization will present a purposeful alternative to
current disposal practices with their associated problems. The
complexity of urban waste economics leads one to the conclusion that
"total system" concepts consisting of waste collection, separation,
utilization and disposal must be considered for logical municipal planning
to take place. The variations in waste due to geographic location,
season, local affluence, etc. dictate local studies in the pre-planning
stage for any community contemplating a new system. National averages
will not be useful for plant designs.
33
-------
THE HYDROLYSIS PROCESS
A. Introduction
THE HYDROLYSIS OF CELLULOSE to produce fermentable sugars was
investigated and utilized in Germany during the periods of World War I
and II. A report summarizing the German industry following World War II
41
Is available from the United States Department of Commerce. Several
processes and their commercial applications are discussed.
Two general processes evolved from the German work: 1) The strong
acid or Bergius Process, and 2) the weak acid or Scholler Process.
The economics of the processes when applied to the saccharification of
wood wastes were evaluated. The Bergius Process showed extremely high
capital costs, which along with high labor and raw material costs on the
U.S. market eliminated its usefulness here. The Scholler Process while
uneconomic in the United States in its original form was considered for
further technical development.
Work on the weak acid hydrolysis of cellulose was performed at the
U.S. Forest Products Laboratory at Madison, Wisconsin during and following
53 54
World War II. The resulting Madison Wood Sugar Process was superior
to the German process on the basis of the productivity rates and product
yields achieved. Pilot and commercial plant operations using various
modifications of the process based on raw materials and final products
1ad
55
53 54
were established at Madison, Wisconsin, Springfield, Oregon ' and
Wilson Dam, Alabama.
B. Chemistry and Kinetics of the Process
In designing the plants for hydrolysis of waste paper the kinetic
data for wood hydrolysis was used. The data was compiled by J.F. Saeman
1+0
of the U.S. Forest Products Laboratory in Madison, Wisconsin.
Kinetically speaking, the hydrolysis of wood to sugar Is a series
reaction, since in the dilute acid process, the sugars decompose at
reaction conditions.
-------
The reaction Is:
Wood cellulose -» Sugars -» Decomposition Products
(A) -» (R) (S)
Let us consider each of the above constituents in order.
The chemical ingredients of wood can be classified as outlined in
Table X. Aside from extraneous materials such as volatile oils, natural
dyestuffs, tannins, etc., wood is composed of a carbohydrate fraction and
a lignin fraction. Lignin is a complicated high polymeric non-carbohydrate.
It is composed largely of aromatic units and makes up 20 to 30 percent
of the weight of wood. Lignin resists hydrolysis in both the dilute-
acid and strong-acid processes and remains as an insoluble residue after
hydrolysis.
TABLE X. QUALITATIVE OUTLINE OF THE COMPOSITION OF WOOD
53
I. Main components of the cell wall
A. Total carbohydrate fraction
1. Alphacellulose
2. Hemicellulose
a. Pentosans
i. Xylans
2. Arabans
b. Hexosans
1. Mannans
2. Glucosans
3. Galactans
c. Uronic acids
B. Lignin
II. Extransous materials
A. Volatile oils and resin acids; volatile acids
B. Fixed oils (fatty oils)
C. Natural dyestuffs and precursors
D. Tannins
E. Polysaccharides and glycosides
F. Ash (mineral salts)
G. Organic nitrogen compounds
H. Other organic ingredients, like resins, phytosterols. etc.
35
-------
The carbohydrate portion of wood accounts for 70 to 80 percent of
the dry wood substance (D.W.S.) and is composed of alphacel lulose and
hemicel lulose as shown in Table X. Alphace! lulose or true cellulose is
a high-polymer substance, composed of multiple glucose units with the
chemical formula (C,H. 0 )n. When complete hydrolysis takes place, the
bonds between glucose units are broken and a molecule of water is added
to each unit to give the sugar glucose. The acid acts only as a catalyst.
alphacel 1 ulose glucose
Table XI gives the percentage composition of various woods. As
shown, alphacel lulose accounts for k$ to 50 percent of the D.W.S. and
hemicel lulose accounts for 20 to 30 percent D.W.S. Hemicellulose, in
addition to alphacel lulose is part of the carbohydrate fraction of wood
and is hydrolyzable to sugars. The distinction between alphacel lul lose
and hemicel lulose is not at all a clear one. Ideally, alphacel lulose
is that part of the total carbohydrate that hydrolyzes to glucose whereas
hemicel lulose hydrolyzes largely to pentose sugars and hexose sugars
other than glucose. In practice, however, hemicel lulose has been defined
as "the easily hydrolyzed portion of the wood". This definition is the
most useful and is the one on which most data is based. Hemicel lulose
hydrolysis gives a much larger percentage of pentose sugars than alpha-
cellulose and its hydrolysis rate is at least an order of magnitude
faster.
There are six sugars obtainable from the hydrolysis of wood. These
are glucose, mannose, ga lactose, fructose, xylose, and arabinose. Table XII
gives the percent of each of these sugars obtained in the hydrolyzate of
various woods. Glucose, mannose, galactose, and fructose are all hexoses
(six carbon sugars) of molecular weight 180. Xylose and arabinose are
pentoses (five carbon sugars) of molecular weight 150. The four hexoses
each have the chemical formula ^-f^irflc and differ only in structure whereas
the two pentoses have the formula C,-H.00_ and also differ in structure.
Sugars are classified two ways: 1) According to their ability to reduce
36
-------
Fehling's or To 11 en's reagent, and 2) according to their fermentabi1ity
by Saccharomyces cerevisiae yeast. All monosaccharides and most di-
saccharides reduce Fehling's or Tollen's reagent and are thus reducing
sugars. Since all sugars obtained by wood hydrolysis are monosaccharides
the reducing power of the hydrolyzate is a measure of the total sugar
content. On the other hand, fermentability is a measure of only the
hexose sugars since S. cerevisiae, traditionally used in brewing, cannot
ferment pentose sugars. However, other yeast strains can utilize a
considerable portion of the pentose sugars. Table XIII gives the
potential reducing sugar and potential fermentable sugar obtainable from
various woods.
TABLE XI. THE PERCENTAGE COMPOSITION OF CERTAIN WOODS
53
White
spruce
Red
spruce
Eastern
hemlock
Balsam
fir
Jack pine
Aspen
Willow
Maple
White oak
Lignin
26.6
26.6
31.5
30.1
27.2
17.3
22.0
23.5
24.1
Holo-
cellu-
lose
73.3
72.9
68.5
69.9
72.5
82.5
78.3
76.3
75.4
Alpha-
eel lu-
lose
49.5
48.3
48.2
44.0
49.5
50.7
50.0
49.5
Hemi-
cel lu-
lose
23.8
24.6
20.3
25.9
23.0
31.8
26.3
25.9
Pento-
sans
10.9
H.6
10.0
10.3
12.8
23.5
Uronic
acid
anhy-
dride
2.68
3.20
3.40
3.08
2.92
4.28
Acetyl
2.35
2.50
1.87
2.24
1.92
4.65
Methoxyl
in
carbohy-
drate
0.70
0.92
0.84
0.41
0.75
0.93
TABLE XII. COMPOSITION OF THE TOTAL HYDROLYZATE OF WOOD
53
Birch
Jack pine
Spruce and p ine
G 1 ucose
Mannose
Ga lactose
Fructose
Xylose
Arab! nose
Total
67.7
1.8
0.0
30.1
0.4
100.0
67.6
14.1
6.2
8.9
3.2
100.0
61.9
24.7
4.0
1.4
8.0
__
100.0
37
-------
TABLE XIII: YIELD OF POTENTIAL REDUCING SUGARS
AND FERMENTABLE SUGARS FROM SAMPLES
OF REPRESENTATIVE HARDWOODS AND
SOFTWOODS 53
Species
Hardwoods
American beech
Aspen
Birch
Maple
Red oak
Sweet gum
Yel low poplar
Softwoods
Douglas Fir
Eastern white pine
Hemlock
Ponderosa pine
Redwood
Sitka spruce
Southern yellow pine
Suqar pine
Potential
reducing
sugars
%
70.1
75.1
69.9
68.2
63.6
66. if
70.9
66.6
66.5
66.1
68.0
52. 4
70.1
64.8
64.3
Ferment-
ability
%
75.1
76.3
67.8
71.0
63.0
73.8
76.1
86.2
86.3
88.2
82.2
77.1
85.3
82.0
82.4
Potential
fermentable
sugars
%
52.6
57.3
47.4
48.4
40.2
49.0
54.0
57.4
57.4
58.3
55.9
40.4
59.8
53.2
53.0
Unfortunately, the reaction conditions that favor wood hydrolysis also
favor sugar decomposition. Qualitively the decomposition reactions are
as follows:
C5H10°5
Pentoses
C6H12°6
Hexoses
C5H4°2 +
Furfural
C6H6°3 +
3H2°
3H2°
Hydroxymethyl furfural
3)
4)
ccH,00, -» C
D I / b 5
., + HCOOH + H 0
3 2
Hexoses Levulinic Formic
acid acid
C6H12°6 or C5H10°5
Hexoses Pentoses
Humic Substances
Sludge
38
-------
The humic substances formed in reaction k are high molecular weight
condensation products. Very little qualitative information is available
on the relative rates of the above reactions and therefore the by-product
production of the plant is somewhat uncertain.
Discussion of Kinetic Data:
^0
Saeman did his kinetic studies on the hydrolysis of Douglas fir
wood chips using dilute sulfuric acid. The hydrolysis rate of Douglas
fir is compared to several other woods in Figure k and is found to be
fairly representative. The kinetic data for Douglas fir was therefore
used as a basis for the plant design. Figure 5 shows the variation of
hydrolysis rate with particle size. As may be expected the reaction rate
increases as the wood chips become smaller or as the exposed surface area
becomes larger. In applying these results to the hydrolysis of waste
paper one would expect the pulped paper to have a larger exposed surface
area than an equal weight of wood chips and therefore a greater hydrolysis
rate. By using the kinetic data for wood chips the calculations are
expected to be somewhat conservative.
In addition to the type of wood used and the particle size of the
wood chips, other process variables of importance are: 1) Liquid to solid
ratio (L/S), 2) acid concentration, 3) temperature, and 4) time. Saeman
studied Douglas fir chips smaller than 30 mesh using the following range
of variables: 1) Liquid to solid ratios from 5:1 to 20:1, 2) acid concentra
tions from Q.k percent (by weight) to 1.6 percent, 3) temperatures from
170 C to 190°C, and k) times from 0 to kQO minutes. Figure 6 shows the
variation of hydrolysis rate with liquid to solid ratio at 180 C and
0.8 percent sulfuric acid. The hydrolysis rate increases with increas-
ing L/S ratio. Figure 7 gives the hydrolysis rate for various acid
concentrations and temperatures. The L/S ratio is 10:1. Figures k
through 7 show consistently that the hydrolysis of wood is a first
order reaction of the form.
5) r, - fA . k,CA
where r = reaction rate
c * concentration
k - first-order reaction rate constant
t * time
39
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RED OAK
DOUGLAS FIR
HARD' MAf»LE
SOUTHERN YELLOW PINE
ASPEN
10
20
TIME (MINUTES)
Figure jj Comparative Rates of Hydrolysis of Various Species of Wood
-------
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Figure 7 Hydrolysis of Douglas Fir at 170°C. 180 and 190
k2
-------
Saeman also presents data on the decomposition rates of sugars.
Figure 8 compares the decomposition rates of various sugars formed by
wood hydrolysis. It is seen that the pentose sugars decompose more
rapidly, particularly xylose, and glucose is the most stable. Figure 9
shows the decomposition rate of glucose as a function of acid concentra-
tion and temperature. From these figures ft is clear that all the sugars
decompose by a first order reaction since a plot of the logarithm of
concentration against time is a straight line. Figures 10 and 11 show
the variation of the first order reaction rate constant (k?) for glucose
with acid concentration and temperature. From these lots one can make
the following correlation for glucose.
8) k, - 1.86 x 1014C U02e "3p'7°° min"1 (Based on loss of
/ S KI
reducing power).
To be completely accurate the decomposition rate of the sugar in
the hydrolyzate should be a weighted average of the decomposition rates
for the individual sugars. Thus k» will change during the reaction from
a relatively large value initially (due to the higher concentration of
pentose which are easily decomposed) to a lower value finally when
glucose is substantially the only sugar formed. Determining what weighted
average to use as a function of time would require considerable specifica-
tion. Since these kinetics deal only with alphacellulose hydrolysis
and since much more glucose is formed than any other sugar in this type
of hydrolysis, the kinetic data for glucose was used to determine the
decomposition rate of the sugars in the hydrolyzate.
The yield of sugar increases as the acid concentration increases
and as the temperature increases. In addition, the yield increases as
the liquid to solid ratio increases. Since high acid concentrations are
undesirable from the stand point of corrosion it would probably be more
profitable to increase yield by increasing the reaction temperature. In
addition use of high concentrations of acid and high liquid to solid
ratios would substantially increase raw material costs unless some means
of acid recovery was employed, and sulfuric acid is difficult to recover.
It is unfortunate that Saeman did not investigate a wider range of
variables, particularly temperature. For the design of the continuous
reactors the data was extrapolated to 200 C, 10 C above the experimental
range.
43
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40 50 60
TIME (MINUTES)
Decomposition of Sugars at 180 C. in
0.8% Sulfuric Acid **°
-------
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Q_
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90
80
7°
60
50
30
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RESIDUAL REDUCING
SUBSTANCES AS GLUCOSE
_RESIDUAL FERMENTABLE
SUGAR AS GLUCOSE
100
150 200 250 300
TIME (MINUTES)
400
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RESIDUAL REDUCING
SUBSTANCES AS GLUCOSE
RESIDUAL FERMENTABLE
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RESIDUAL REDUCING
SUBSTANCES AS GLUCOSE
RESIDUAL FERMENTABLE
SUGAR AS GLUCOSE
20
-"N-
30 40 50 60
TIME (MINUTES)
70
80
Decomposition of Glucose in Dilute Sulfuric Acid
at 170°, 180°, and 190°C. **°
45
-------
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k BASED ON LOSS OF FERMENTABLE SUGAR
k BASED ON LOSS OF REDUCING POWER
0.2 O.*t 0.8 1.6 3.2
SULFUR 1C ACID CONCENTRATION (PERCENT)
Figure lo Relation of First-Order Reaction
Constant k to Acid Concentration in Decomposition
of Glucose at Various Temperatures
-------
0.2
0.1
0.09
0.08
0.07
0.06
0.05
0.03
0.02
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k BASED ON LOSS OF FERMENTABLE SUGAR
k BASED ON LOSS OF REDUCING POWER
0.00215
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0.00230
THE RECIPROCAL OF THE ABSOLUTE TEMPERATURE
Figure II Relation of First-Order Reaction Constant k to
Temperature in Decomposition of Glucose with Sulfuric Acid
of Various Strengths ^°
-------
C. The Batch Process
The U.S. Forest Products Laboratory of Madison, Wisconsin did
54
considerable work on wood saccharification during World War II. The
work was authorized by the War Production Board to find a commercially
practical method of obtaining sugar from wood and subsequently fermenting
the sugar to alcohol. The process recommended by the Forest Products
Laboratory was called the Madison Wood Sugar Process and used semi-batch
digesters or percolators for reactors. These are simply towers or
pressure tanks into which a batch of wood chips is charged. The liquid
phase (0.5 percent sulfuric acid solution) is then introduced continu-
ously, allowed to flow down over the wood chips, and withdrawn continu-
ously during the percolation period. When the sugar in the hydrolyzate
leaving the reactor falls below 1 percent, the liquid is drained from
the spent wood chips which are subsequently discharged.
The Forest Products Laboratory also investigated a reaction scheme
similar to one patented by Scholler in Germany. This scheme consisted
of charging wood chips to a digester and then introducing a given amount
of dilute acid, allowing the reaction to occur for a specific time, and
draining off the hydrolyzate. This is followed by the introduction of
fresh acid solution and the cycle is repeated until the sugar in the
hydrolyzate drops below a predetermined value. Although the Forest
Products Laboratory reaction scheme was similar to the German Scholler
process, reaction conditions were quite different and the American
process gave better yields in less time.
The following is a comparison by the Forest Products Laboratory of
the Madison Wood Sugar Process, the German Scholler process, and the
54
American modified Scholler process.
"A process, known as the Madison wood sugar process, has
been developed for hydrolyzing mixtures of wood waste with
0.5 percent to 0.6 percent sulfuric acid at 150°C to 180°C by
allowing the dilute acid to flow continuously through the charge
of wood. Compared to the German Scholler process, hydrolysis was
accomplished in less time because the sugars produced were removed
more rapidly. Decomposition was less because the sugars were in
contact with the acid for a shorter period of time and consequently,
yields of sugar and alcohol were higher. Fewer by-products
inhibitory to fermentation were produced, so that fermentations
48
-------
were more rapid. The sugar produced in 2.8 hours from a ton of
dry, bark-free, Douglas fir wood waste yielded 64.5 gallons of
95 percent alcohol as compared to 3.2 hours for 58 gallons by the
rapid cycle method developed earlier, (American modified process)
and 13 to 20 hours for 55 gallons by the Scholler process as
carried out in Germany.11
The Madison wood sugar process was clearly superior to all other
batch processes and a plant using the Madison process was constructed
at Springfield, Oregon. A description of this plant has been given by
53 5k
several authors. ' The plant was a 78 fold scale up of the Forest
Products pilot plant. Several difficulties were encountered in its opera-
tion and consequently the Tennessee Valley Authority at Wilson Dam,
Alabama undertook a study of the process on a scale intermediate between
the Forest Products Laboratory and the Springfield plant. The T.V.A. made
several simplifying recommendations and improvements. Their pilot
plant was designed to hydroly?e wood chips to sugar and then concentrate
the sugar solution to 50 percent molasses for use in animal fodder. The
commercial plant proposed as a result of T.V.A. pilot plant work is
shown in Figure 12. In general, the wood hydrolysis portion of the plant
(excluding evaporation and concentration) is quite similar to the
Madison wood sugar process. The TVA modification of the Madison process
was followed quite closely in the design of our batch hydrolysis plant.
Unfortunately, neither the Springfield plant nor the proposed TVA
plant had economic data which allowed one to estimate the cost of the
hydrolysis portion of these plants.
Batch Process Description:
The flow sheet for the proposed batch process is given in Figure 13.
Using one 2000 cubic foot digester, based on the maximum size of the
Springfield, Oregon plant, plant capacity and operating procedures were
determined.
The total operating time per batch is 4.75 hours. It is possible
to run five batches per day using this time schedule, and since each
batch uses 16 tons of dry wood substance the plant will handle 80 tons
of raw material per day.
49
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The Processing of a Single Batch:
1. The digester is filled with wood chips (or paper pulp),
packed with a sudden steam blast, and refilled. The charge
is heated with live steam, to an initial temperature of 300 F
(pressure = 67 psia); the condensate remains in the digester.
This requires about k tons of steam.
2. Hydrolyzate collected during the drain period of the previous
batch is introduced as rapidly as possible. The 17.2 tons of
recycled solution is composed of 1 percent reducing sugars,
0.^3 percent sulfuric acid, and the remainder largely water with
some decomposition products,
3. As the recycled hydrolyzate is being introduced sulfuric acid
must also be introduced in a quantity of 0.101 tons of 77.7 percent
(60 Baume) sulfuric acid per batch. This make-up acid is required
for two reasons: The acid concentration in the recycled hydrolyzate
is below 0.5 percent due to the fact that some sulfuric acid
combines chemically with lignin, and the steam condensed during
packing and heating must be brought up to a 0.5 percent acid
concentrat ion.
4. The digester contents are held at 300°F for 15 minutes during
which the hemicellulose hydrolyzes. The liquid to solid ratio is
2 to 1.
5. At the end of this period the hydrolyzate line at the bottom of
the digester is opened and the hydrolyzate is drained at a rate of
200 gal/min. At the same time, dilute acid is introduced into the
top of the digester at 200 gal/min. The temperature of the dilute
acid used for percolation is controlled by the injection of 250 psi
steam.
6. The temperature of the dilute acid being introduced is raised
from an initial temperature of 300 F to a final temperature of 380 F.
-------
The rate of temperature rise Is 5°F/minute taking a total of 16
minutes. Dilute acid at 380°F is introduced at 200 gal/min. for
the remainder of the percolation period (13^ minutes). Hydrolyzate
is continuously withdrawn during the same period.
7. The hydrolyzate is flashed to atmospheric pressure in a series
of 2 flash tanks. The first tank operates at 65 psia and the
second at atmospheric pressure. The first hydrolyzate to be
withdrawn from the digester is at a temperature of 300 F (6? psta)
and thus very little is vaporized in the first flash tank. As the
hydrolyzate temperature increases, the fraction vaporized in the
first flash tank increases to 0.09^3. The fraction vaporized in
the second flash tank is constant at 0.0902.
8. By the end of the percolation period the sugar content of the
hydrolyzate has dropped below 1 percent. The liquid in the digester
is then drained. About 25 percent of the drained hydrolyzate is
flashed while the remainder is sent to a hold-up tank and subsequently
recycled to the next batch of fresh wood chips for the hemicellulose
hydrolysis.
9. After the draining period, the spent wood chips (mostly lignin)
are blown down to atmospheric pressure through a quick opening valve
in the bottom of the digester.
10. The vapors produced in the flashing process are condensed by
counter-current heat exchange with water to be used in the
digester. This considerably reduces the steam required for heating
the dilute acid stream.
11. Humic substance formed as a result of sugar decomposition
separates out in the flash tanks as a thick insoluble sludge.
12. The hydrolyzate, still containing about 0.5 percent sulfuric
acid is then neutralized with calcium carbonate to form a calcium
sulfate precipitate. Since the solubility of calcium sulfate
decreases as the solution temperature increases it is desirable
to maintain the hydrolyzate at a high temperature. The neutralizer
53
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serves two purposes: a) to contact the hydrolyzate with limestone
and b) to provide a hold-up in the process so that the slurry may
be removed continuously.
13. Calcium sulfate and excess calcium carbonate are removed from
the system by centrifugatIon. The hydrolyzate leaving the centrifuge
contains about 6 percent reducing sugar. Thus the plant will take
80 tons per day of dry wood substance and convert it to 34.1 tons of
sugar.
The conversion of wood to sugar (based on the DWS charged to the
reactor) is 43 percent. This number was taken from the TVA proposed plant
and is based on their pilot plant work. Even though it is theoretically
possible to calculate the conversion from Saeman's kinetics, the complexity
of the system requires several questionable assumptions and the resulting
differential equations are quite complex. Therefore the experimental
conversion was used.
Economic Analysis:
The required process equipment together with description, material
of construction, and costs is listed in Table XIV. Further specifications
in addition to assumptions made in the design of the equipment are included
with the calculations in the addendum report on hydrolysis. The cost
indicated for a piece of equipment in this table is the arithmetic average
f *,, ,. f . c 57,58,59,60,61,62,63,64,65,66,67,68
of the costs from various references. "'-' »-'-'» » » » " » '» » '»
All costs are corrected to a Chemical Engineering Plant Cost index (CE)
of 100 (1957-1959 = 100) 9and are on an installed basis. Where installation
costs were not given a value of 43 percent of the purchased equipment cost
was used. This value is recommended by various authors. '
The total installed equipment cost (CE = 100) is $332,400. From January
through June, 1967, the Chemical Engineering Plant Cost Index has
remained approximately constant at 109. Correcting to an index of 109,
then, the installed equipment cost is $362,000. Table XV is an estimate
of the required total capital investment. An explanation of the various
items included in this estimate immediately follows Table XV. The total
54
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TABLE XIV: AVERAGE EQUIPMENT COSTS
Item
Size
Material of
Construct ion
Installed Cost
C.E. Index = 100
1) H.SO. Storage Tank
2) H SO, Feed Tank
3) Limestone Storage Tank
k) Neutralizer
5) 2-Condensers
6) 2-Flash Tanks
7) Blow-Down Tank
8) Recycle Storage Tank
9) Digester
10) Centrifuge
11) Pump + Drive #1
12) Pump + Drive #2
13) Pump + Drive #3
\k) Pump + Drive #k
15) Pump + Drive #5
16) Pump + Drive #6
17) Pump + Drive #7
18) Lignin Conveyor
19) Limestone Conveyor
19,000 Gal.
625 Gal.
21,000 Gal.
21,000 Gal.
200 ft2 each
500 Gal each
11,200 Gal.
4,860 Gal.
2000 ft3
30 in. Bowl Dia.
kO GPM
0.73 GPM
\kk GPM
16 GPM
158 GPM
200 GPM
200 GPM
200 ft long
200 ft long
Monel-Clad Steel 23,300
Monel-Clad Steel 3,600
Steel 8,200
Steel (Agitated Tank) 20,700
Steel Shell-Stainless Steel 13,500
Stainless-Clad 15,800
Monel-Clad Steel 15,800
Stainless-Clad 26,600
316 Stainless 133,000
Steel 31,700
Stainless 1,600
Stainless 1,400
Stainless 2,100
Iron 1,400
iron 4,000
Stainless 2,500
Iron 1,700
Open Belt 12,600
Open Belt 12,900
Total Equipment Cost (installed 1957-1959) 332,400
The Chemical Engineering Plant Cost Index for 19&7 from January through
June has remained approximately constant at 109.
Total Installed Equipment Cost (CE = 109) = 362,000
55
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TABLE XV: ESTIMATE OF TOTAL CAPITAL INVESTMENT - BATCH PROCESS
ITEM & BASIS OF ESTIMATE COST (CE = 109)
1. Purchased Equipment - Delivered (P.E.G.) 253,000
2. Equipment Installation (Including Instrumentation
and Insulation) - k3% P.E.G. 109.000
Installed Equipment Cost 362,000
3. P.iping (Including Insulation) 36% P.E.C. 91,000
4. Electrical Installations 15% P.E.G. 38,000
5. Buildings Including Services 35% P .E.C. 88,500
6. Yard Improvements 10% P.E.C. 25,300
7. Service Facilities 35% P.E.C. 88,500
8. Land 6% P.E.C. 15.200
Total Physical Plant Cost 718,500
9. Engineering and Construction kQ% P.E.C. 101.200
Direct Plant Cost (D.P.C.) 819,700
10. Contractor's Fee 7% D.P.C. 57,500
11. Contingency 15% D.P.C. 123.000
Fixed Capital Investment (F.C.I.) 1,000,200
12. Working Capital (Total Operating Cost for 30 Days) 9^.000
Total Capital Investment 1,09^,200
56
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physical plant cost was estimated to be $718,500. The fixed capital
investment was $94,000 to give a total capital investment of $1,094,000.
For the sake of comparison the TVA work claimed that the installed
equipment cost of the hydrolysis section (excluding neutralization and
centrifugation) was $114,200 for a 50 ton per day plant at an Engineering
News Record Index of 542. Correcting this to an 80 ton per day plant
using the six-tenths factor gives $151,500. At a Chemical Engineering
Index of 109 the cost is $232,000. The cost of the neutralizer and
centrifuge (CE Index » 109) is $57,200, for an estimated cost of $289,200
for the installed equipment, compared to $362,000 as estimated in this
paper.
Explanation of Total Capital Investment Estimate - Table XV:
Item 1 - Purchased equipment costs were obtained from various
,: 57,58,59,60,61,62,63,64,65,66,67,68 ..
references. Since some
references listed the cost of installed equipment all costs
were put on an installed basis. The arithmetic average of
the costs from the various references was taken as the
equipment cost. All costs were corrected to a Chemical
Engineering Plant Cost Index of 100 and these are summarized
in Table XIV. The total installed equipment cost was then
corrected to the present (June, 1967) CE Index of 109 and
the purchased equipment cost was obtained from this by
assuming an installation cost of 43 percent of the purchased
equipment cost.
Item 2 - Lang reports a study based on the design of 14 different
chemical plants. This study indicates that about 70 percent
of the installed equipment cost is spent for the equipment
while about 30 percent is spent on installation. Thus on
the basis of purchased equipment costs installation is jr
or about 43 percent. This value includes instrumentation,
insulation, foundations, supports, platforms, and erection
of the equipment.
57
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Item 3 - Piping costs for plants handling both solids and liquids
are estimated at 36 percent of the purchased equipment
cost.5 ' P 9 This includes both material (21%)and labor
(15%).
Item 4 - In ordinary chemical plants the cost of electrical installations
amounts to 10 to 15 percent of the value of all purchased
equipment.5 ' P 97 "Electrical installations" consist primarily
of material and installation labor for power and lighting.
Item 5 - "Buildings including Services" consists of expenses for
labor, materials, and supplies involved in the erection
of all buildings connected with the plant in addition to
such building services as plumbing, heating, lighting, and
ventilating. The cost of this item depends largely on
whether a large portion of the major equipment is located
indoors or outdoors. Assuming largely outdoor construction
a value of about 35 percent of the purchased equipment cost
is applicable.58' p 101
Item 6 - "Yard improvements" includes costs for fencing, grading, roads,
sidewalks, railroad sidings, landscaping, and similar items.
For chemical plants this item is usually 10 to 15 percent to
the purchased equipment cost. P
Item 7 - Service facilities include utilities for supplying steam,
water, power, compressed air and fuel in addition to waste
disposal, fire protection, and miscellaneous service items
such as shop, first-aid, and cafeteria equipment and
facilities. The service facilities vary widely depending
on the particular plant requirements. The cost of service
facilities usually ranges from 20 to 70 percent of the
purchased-equipment cost. ' " For a solid-fluid-processing
plant a value of 35 percent was considered applicable. p
Since this plant uses a considerable amount of steam, steam
utilities costs are included in the steam cost. In addition,
since electrical usage is relatively small it was decided
58
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to purchase power from an outside source rather than installing
utilities for self-generation. No fuel or compressed air is
required in this plant which leaves water-supply as the only
remaining utility. In this case then, a value of 35 percent
of the purchased equipment cost is probably a conservative
est imate.
I tern 8 - Land costs may vary from $300 per acre in some rural districts
to $5000 per acre in industrialized areas. Land costs generally
average about 1 to 2 percent of the total capital investment
or about 6 percent of the purchased equipment cost.
I tern 9 - "Engineering and Construction" includes the costs for construction
design and engineeeing, field offices, field supervision,
insurance, temporary construction, inspection, and general
construction overhead. This cost generally ranges from 10 to 20
percent of the total physical plant cost or an average of about
kO percent of the purchased equipment cost.
I tern 10 - The contractors fee varies with the complexity of the plant but
is ordinarily in the range of k to 10 percent of the direct plant
cost. ' An average value of 7 percent was chosen.
Item II - A contingency factor is usually included in a capital investment
estimate to account for such unforeseen expenses as storms,
floods, strikes, price changes, small design changes, errors in
estimation, and so forth. Contingency factors usually range
from 10 to 20 percent of the direct plant cost. An average
value of 15 percent was used.
Item 12 - Working capital consists of money invested in the following: 1) raw
materials and supplies carried in stock, 2) finished products and
semifinished products in stock, 3) accounts receivable, and k)
cash which must be kept on hand for monthly payment of operating
expenses such as salaries, wages, and raw material purchases. The
raw-material inventory usually amounts to a 1-month Supply.
No finished or semi-finished products are stocked in any appreciable
amount in this section of the plant. No product is sold to a
customer which eliminates accounts receivable. In this case, then,
59
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the working capital consists of 1 and ^ above. A good
approximation for working capital would be the total
production cost for 1 months operation. Working capital is
usually about 10 to 20 percent of the total capital investment. '
Manufacturing Costs:
The estimated manufacturing cost for hydrolyzate sugar from a plant
utilizing wastepaper as feedstock is given in Table XVI. The daily manufact-
uring cost was estimated to be $3.133. No allowance was made for the value
of the calcium sulfate which is a product of the neutralization reaction.
About 3.19 tons per day of calcium sulfate are produced but the solid product
contains impurities as well as an equal weight of water. In order to sell
the produce, provisions would have to be made for drying, storing, and shipping.
The daily output of sugar from this hydrolysis plant is 68,300 pounds.
This number must be modified however to allow down-time for maintenance
work, unforseen work stopages, etc. Assuming an on-stream factor of 0.9
or 328 days of full capacity operation per year, the average daily production
is 61,500 pounds of sugar. The cost per pound of sugar is then 5.1 cents.
Explanation of Estimated Manufacturing Cost - Table XVI:
Item A-l - The f.o.b. costs, freight rates, and assumptions made
in the calculation of raw material costs are given in
the addendum report on hydrolysis.
I tern A-2 - The calculation of utility costs and the assumptions made
in these calculations are given in the addendum report.
I tern A-3 - The operating labor force of k men/shift was based on the
following expected requirements.
1) Two men to operate the digester
2) One man to attend the flash tanks, condensers, and sludge
separators.
3) One man to operate the neutralizer and centrifuge. It is
doubtful that the plant operation will fully occupy the 4
men. Therefore, in their spare time these men can run control
tests.
60
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TABLE XVI: ESTIMATED MANUFACTURING COST - BATCH PROCESS
ITEM UNITS/DAY COST
A. Direct Production Costs
1 . Raw Materials <
H,SO. (60° Baume = 77-7%) 4.38 Ton *26.00/Ton
Limestone (Crushed - 100 Mesh) 3.83 Ton 12.40/Ton
Wastepaper (Mixed) 80.0 Ton 13.00/Ton
2. Utilities §
Electricity (125% of Process Demand) 2580 kw-hr * 0.014/kw-hr
Steam (125% of Process Demand) 144/Ton 0.75 Ton
Process Water 162.5 M-Gal 0.25/M-Gal
3. Operating Labor 4 Men/Shift 96 Man-Hrs. * 3.00/M-Hr.
at $3.00/Hr.
4. Supervisor 1 Man - Day Shift 8 Man-Hrs. "* 3.50/M-Hr.
at $3.50/Hr.
5. Fringe Benefits
15% of Operating Labor + Supervision
6. Operating Supplies, 10% of Labor
7. Maintenance and Repairs, 10% F.C.I.
Labor (per year) = 5% F.C.I.
Overhead & Supplies (per year) = 5% F.C.I.
Direct Production Cost
B. Fixed Charges
1. Depreciation - 12 Year Plant Life - Zero Salvage
Value » 8 1/3 % F.C.I, per year
2. Local Taxes 2% F.C.I, per year
3. Insurance 1% F.C.I, per year
Fixed Charges
C. Plant Overhead - 70% of Operating + Maintenance
Labor + Supervision = (.70) (440)
D. General Expenses
1. Administrative Costs - 15% of Operating
+ Maintenance Labor + Supervision = (.15) (440)
2. Distribution and Selling Cost - (Not Applicable)
3. Research and Development Cost - 5% Total Product Cost
4. Financing Interest 4% of Total Cap. Invest. Per Year
General Expenses
Total Production Cost (A -t- B + C * D) »
DAILY COST
125.60
^7.50
1,040.00
36.10
216.00
40.60
288.00
28.00
47.50
28.80
137.00
137.00
2,172.10
228.00
54.80
27.40
310.20
308.00
66.00
-
157.00
119.00
343.00
3,133.30
Assuming an On-Stream factor of 0.9 to allow down-time for maintenance and other
unforseeable work stoppages the average daily output is 61 ,500#Sugar
to 17-3
Total Product Cost=K' ^iu = 5.U/#Sugar
61
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Item A-5 - Generally, fringe benefits range from 10 to 25 percent
of the straight hourly wage. ' " An average value
of 15 percent was assumed.
Item A-6 - Operating supplies include such miscellaneous expenses
as gloves, stationery, flashlights, wiping rags, etc.
This item varies from about 5 to 20 percent of the operating
labor and an average value of 10 percent is usually
72
applicable.
Item A-7 - Maintenance and repairs usually range from k to 8 percent
of the fixed capital investment per year. For a plant
handling corrosive materials this may go as high as 12
72
percent. A value of 10 percent was chosen. Fifty to
sixty-five percent of the total maintenance can be
72
attributed to maintenance labor. A value of 50 percent
was taken.
Item B-l - Depreciation was calculated on the basis of a 12 year plant
life with zero salvage value to give 8-1/3 percent per year.
Interest on the investment was taken into account in item
D-*f. Eight and one-third represents a fairly typical
72 73
depreciation allowance.
Items B-2 and B-3 - Local taxes range from 1 to k percent of the
fixed capital investment per year while insurance varies
from 0.1* to I percent per year. ' ^ Respective values
of 2 and 1 percent were selected.
Item C - Plant overhead is usually in the range of 50 to 70 percent
of the cost for operating labor, supervision, and
maintenance labor. ' " Another source indicates
50 to 100 percent of the productive payroll. Therefore
a value of 70 percent was chosen. Plant overhead includes
the following: general plant upkeep, payroll overhead,
packaging, medical services, safety and protection,
restaurants, recreation, salvage, laboratories and storage
facilities.
62
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Item D-l - Administrative Costs includes costs for executive salaries,
clerical wages, legal fees, office supplies, and communications.
The cost amounts to about 15 percent of the operating labor,
supervision, and maintenance labor.
Item D-2 - This item was not considered applicable since no product
was being sold or distributed.
Item D-3 - Two to five percent of every sales dollar goes toward
financing research and development or approximately 5 percent
of the total product cost. ' P Although this item is
questionable in this application it remains in the analysis
as a second contingency factor in keeping with the conservative
approach to estimating operating costs.
Item D-4 - Some factor should be applied to take into account the time-
value of money. The money borrowed for the fixed capital
investment is paid back gradually over the life of the plant
by depreciation allowances. The investment made on the
working capital is not regained until the plant is shut
down. The financing interest takes into account the interest
paid on the money borrowed for both the fixed capital and
working capital investments. It is approximately k percent
per year of the total capital investment. The actual
interest payments of course, will be greater than this
in the early years of the plant life and smaller in the
later years.
63
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D. The Continuous Process
The flow sheet for the continuous process is shown in Figure \k.
In general this process is similar to the batch process and requires the
same processing steps: hydrolysis, flash vaporization, neutralization,
and centrifugation. The basic difference is in the reactor. The continuous
reactor system is a series of individual reactor tubes with a screw press
after each unit. Paper pulp and dilute acid are conveyed co-currently
through each reactor tube by means of a screw conveyor. Paper pulp containing
50 percent moisture from pre-hydrolysis processing is fed to reactor number 1.
A hot dilute solution of sulfuric acid mixes with the paper pulp at the
inlet of the reactor and heats the charge. The first reactor is designed
to hydrolyze only the hemicellulose portion of the charge and should
therefore be operated at lower temperatures and shorter residence times
than the other reactors to minimize the decomposition of the sugars. An
initial liquid to solid ratio of k was used. From reactor number one the
paper pulp-dilute acid mixture passes through a screw press that squeezes
most of the hydrolyzate from the paper pulp thus removing from the reaction
system most of the sugars formed in the first reactor and preventing their
decomposition: The paper pulp from the screw press containing about 50
percent, moisture is mixed again with fresh, hot, dilute acid at the inlet
of reactor number 2. The temperature of reactor two is maintained at
200 C since this and all remaining reactors are designed to hydrolyze the
alpha cellulose portion of the charge. The residence time is longer, about
10 minutes, and corresponds to the residence time at which conversion of
alpha cellulose to sugar is a maximum, Hydrolyzate is again removed by a
screw press after reactor two to prevent further decomposition of sugars.
This scheme of mixing the charge with fresh acid, reacting and removing
the hydrolyzate may be continued for as many stages as economics justifies.
The reactor system described above is commercially available from
74
The Black Clawson Company of Middletown, Ohio. Black Clawson was consulted
for information on costs, operating labor and power requirements, for their
systems used in this plant design.
Reactor one operates at a lower temperature than the other reactors
therefore the hydrolyzate removed from screw press one will be under a
lower pressure.
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13
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Thus the hydrolyzate from screw press one must be pumped to a higher
pressure before mixing with the hydrolyzates from the other screw presses,
resulting in an additional operation.
Other flow sheet changes were made simply to facilitate continuous
addition of hot, dilute, sulfuric acid to each reactor. Aside from the
above mentioned modifications the process description for the batch plant
is generally applicable.
Continuous Process - Discussion of Process Variables:
The important process variables are: 1) residence time 2) temperature
3) Liquid to solid ratio and 4) acid concentration. Residence time is
not an independent variable. That is, given a temperature, a liquid to
solid ratio, and an acid concentration, one can calculate the residence
time at which conversion of cellulose to sugar is a maximum. The equation
for the residence time at which maximum conversion is realized is a
function of initial concentrations and k. and k~, the specific reaction
rate constants for wood hydrolysis and sugar decomposition respectively.
The values of k. and k_ are in turn, functions of temperature, acid
concentration, and liquid to solid ratio. Therefore the optimum residence
time is dependent on these three variables.
The conversion of wood cellulose to sugar increases as the ratio of
k] to k. increases. This ratio can be increased by increasing either
temperature, liquid to solid ratio, or acid concentration. The reaction
temperature can easily be increased by using more steam. However, it is
necessary to keep the dilute acid in the liquid phase; so the pressure
within the reactor must also be increased to correspond with the vapor
pressure of water at the temperature in question. Since vapor pressure
increases exponentially with temperature, operation at high temperature
may lead to excessive pressures. From Figure 15 the vapor pressure of water
at 200°C is 225 psia but at 210°C the pressure is 276 psia. The Black
Clawson Chemipulpers are produced in 2 pressure series: 175 psia and 275
psia. Operation at or above 210 C would require specially fabricated
equipment. Allowing a 10 C safety margin, one could operate at 200°C
and remain within the pressure limitations of the system. Another
66
-------
in
-------
consideration that supports the choice of 200°C as the maximum operating
temperature is the fact that the maximum temperature used to obtain the
o UO
kinetic data was 190 C. It is never a good idea to extrapolate kinetic
data too far from the experimental range. At temperatures below 200°C
both conversion and reaction rate decrease. Reaction rate is quite
dependent on temperature. In the range of 170 C to 190 C an increase of
10 C in the reaction temperature increases the rate of hydrolysis by
186 percent. Thus as one decreases the operating temperature from 200 C
the required reactor volume increases quite rapidly. For example, the
residence time at which conversion of alphacellulose to sugar is a
maximum for acid concentrations of 0.5 percent and liquid to solid ratios
of 10 is as follows:
T = 200°C t max = 11.7 min.
T = 170°C t max = 175 min.
This time is directly proportional to reactor volume for a given feed
rate.
Total steam costs account for only 4.5 percent of the total
manufacturing cost at an operating temperature of 200 C. The cost of
the small amount of steam required to increase the reaction temperature
from 170 C to 200 C will be more than compensated for by a smaller and
less expensive reactor system and an increase in sugar yield. Therefore,
the temperature for alphacellulose hydrolysis was set as 200 C.
Liquid to solid ratio has no effect on k_ (sugar decomposition) and
only a slight effect on k, (alphacellulose hydrolysis). However, it has
a considerable effect on the final sugar concentration, the sugar yield,
and the amounts of acid, water, and steam required for the hydrolysis.
Thus the L/S ratio is quite important. From the standpoint of limiting
acid, water and steam usage the L/S ratio should be small. However from
the standpoint of yield the L/S ratio should be large. This is due to
the fact that a certain amount of liquid is entrained with the solids
and does not get removed in the screw press. The higher the L/S ratio,
the less concentrated the entrained liquid is, and there is less loss of
sugar and therefore a greater yeild. The factor that determines the lower
limit of the L/S ratio is the ability of the screw press to remove the
68
-------
liquid. A single stage screw press can accept consistencies of 15 to
7L
25 percent solids and thicken up to 50 percent solids. Thus the lower
limit on the L/S ratio is 1.0 (50 percent liquid, 50 percent solids).
If the system were operated at this minimum no product would be obtained.
Therefore, higher ratios must be employed. The ratios are determined by
an economic balance of sugar yield against acid, steam, water, and
limestone usage. It should also be pointed out that as the L/S ratio
increases the size of all the process equipment (except the pre-hydrolysis
operations) must also increase. This factor must also be considered. The
optimum L/S ratio probably lies somewhere between 2 and 6. A value of 4
was chosen for this preliminary estimate and the plant was designed on
that basis.
The influence of acid concentration on product cost is summarized
in the following examples. Calculations for this comparison are included
in the addendum report.
A four-stage reactor system using 0.5 percent sulfuric acid converted 100
pounds «f dry feed to 46.57 pounds of sugar whereas the same reactor system
using 1.5 percent sulfuric acid converted the same feed to 49.30 pounds of
sugar. Neglecting the small additional investment for the 1.5 percent
sulfuric acid (for larger storage tanks), the optimum acid concentration
is the concentration at which the daily profits are a maximum. On the basis
of an 80 ton per day plant, the additional sugar produced by using 1.5
percent sulfuric acid is 0.091 tons per hour or, assuming an on-stream
factor of 0.9, 3,930 pounds per/day. From Table XIX the 0.5 percent acid
process requires 4.65 tons of acid per day at a cost of $121. The 1.5
percent acid process would require 3.95 tons of acid per day at a cost of
$363 per day. Also, the 0.5 percent acid process requires 4.42 tons per
day of limestone at a cost of $54.80 per day whereas the 1.5 percent acid
process would require 13.26 tons per day of limestone at a cost of $164.40.
Therefore, the cost of the sugars produced by increasing the acid concentration
from 0.5 to 1.5 percent is:
$(363 + 164.40) - $(121 + 54.80) = 8.95 cents
3,930 pounds sugar pound sugar
From Table XIX, the manufacturing cost using 0.5 percent sulfuric acid is
5.7 cents per pound sugar. Obviously, then, o,ne should not increase the
acid concentration. The total manufacturing cost using an acid concentration
69
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of 1.5 percent turns out to be 5.90 cents per pound sugar. There may be
some economic advantage In decreasing the acid concentration below 0.5
percent but at these low concentrations acid costs are not a major factor
in the manufacturing cost. For example, at Ot.5 percent, the acid cost is
only 3.2 percent of the manufacturing cost when a four-stage reactor
system is used. For this reason no lower acid concentrations were
investigated and the plant was designed on the basis of 0.5 percent sulfuric
acid.
Having chosen the important process variables: T = 200 C, L/S » k,
and acid concentration = 0.5 percent the plant design and economics can
proceed. Actual plant calculations, necessary assumptions and equipment
selections are detailed in the addendum report.
Continuous Process - Economic Analysis:
The equipment costs as found in various references57'58'59'60'61'62'63'
65,66,67,68,75,76^ Summarf2ed in Table XVU. The total installed equipment
cost is $697,000 computed at a Chemical Engineering Plant Cost Index (CE) of
109 (first half, 1967). The reactor system was by far the most expensive
item; its installed cost at CE of 109 was $500,000. The estimated total
capital investment is itemized in Table XVIII. The items included in this
table are defined in the text following Table XV. Several things should
be pointed out concerning this estimate: 1) Many of the items of this
table are based on a percentage of the purchased equipment. Since much of
the plant is constructed of exotic materials (Carpenter 20 for the reactor
system for example) the purchased equipment cost will be much higher than
for the "ordinary chemical plant" on which the estimates are based. That
is, "buildings and services" are estimated at 35 percent of the purchased
equipment cost whether the equipment is constructed of carbon steel or
stainless. This leads one to the conclusion that buildings and services
are a function of the material of construction of the process equipment.
This is, of course, not the case. The 35 percent is based on averages
throughout the chemical process industries and applies strictly only to
the "average chemical plant". To minimize this effect, the installed
equipment cost was calculated and, assuming an installation cost of
70
-------
TABLE XVII: AVERAGE EQUIPMENT COSTS FOR CONTINUOUS
PROCESS USING A FOUR-STAGE REACTOR SYSTEM
Item
Size
Material of
Construction
Instal led Cost
C.E. Index = 100
1) Reactor System
2) 4-Reactor Tube Motors
3) Pre-Hydrolysis Press Motor
k) Screw Press #1 Motor
5) Screw Press #2 Motor
6) Screw Press #3 Motor
7) Screw Press #k Motor
8) H_SO. Storage Tank
9) Limestone Storage Tank
10) Neutralizer
11) 2-Condensers
12) 2-Flash Tanks
13) Centrifuge
\k) Lignin Conveyor
15) Limestone Conveyor
16) Pump + Drive #1
17) Pump + Drive #2
18) Pump + Drive #3
19) Pump + Drive #k
20) Pump + Drive #5
21) Pump + Drive #6
22) Pump + Drive #7
23) Pump + Drive #8
2k) Pump + Drive #9
10 H.P. Each
261 H.P.
202 H.P.
132 H.P.
105 H.P.
98 H.P.
20,500 Gal.
2k,5QQ Gal.
10,800 Gal.
100 Ft2 Each
300 Gal. Each
30 in. Bowl Dia.
200 Ft. Long
200 Ft. Long
31 GPM
26 GPM
17 GPM
\k GPM
k6 GPM
> 1 GPM
107 GPM
97 GPM
97 GPM
Carpenter #20 Steel 459,000
A.C. - Enclosed 5,200
A.C. - Enclosed 10,000
A.C. - Enclosed 7,500
A.C. - Enclosed k,kOO
A.C. - Enclosed 3,500
A.C. - Enclosed 3,^00
Monel-Clad Steel 2^,000
Steel 8,900
Steel (Agitated Tank) 13,800
Steel She!l-Stainless Tubes 9,100
Stainless Clad 16,^00
Steel 31,700
Open Belt 12,600
Open Belt 12,900
Stainless-Centrifugal 1,800
Stainless-Centrifugal 1,800
Stainless-Gear 1,700
Stainless-Gear 1,600
Stainless-Centrifugal 1,900
Stainless-Gear 1,^00
Iron-Centrifugal 3,500
Stainless-Centrifugal 1,900
Iron-Centrifugal 1,^00
Total Equipment Cost - Installed (1957-1959) = 639,^00
For the first half of 1967 a Chemical Engineering Plant Cost Index
of 109 is applicable.
Total Equipment Cost - Installed = 697,000
71
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TABLE XVIII: ESTIMATE OF TOTAL CAPITAL INVESTMENT
FOR CONTINUOUS PROCESS USING A FOUR-STAGE REACTOR SYSTEM
Item & Basis of Estimation Cost (CE = 109)
1. Purchased Equipment - Delivered (P.E.C.) 487,000
2. Equipment Installation (Including Instrumentation
and Insulation) - 43% P.E.C. 210.000
Installed Equipment Cost 697,000
3. Piping (Including Insulation) - 36% P.E.C. 175,000
4. Electrical Installations - 15% P.E.C. 73,000
5. Buildings Including Services - 35% P.E.C. 170,000
6. Yard Improvements - 10% P.E.C. 48,700
7. Service Facilities - 35% P.E.C. 170,000
8. Land - 4% P.E.C. 19.500
Total Physical Plant Cost 1,353,200
9. Engineering and Construction 40% P.E.C. 195.000
Direct Plant Cost (D.P.C.) 1,548,200
10. Contractors Fee 7% D.P.C. 108,200
11. Contingency 15% D.P.C. 232.000
Fixed Capital Investment 1,888,400
12. Working Capital (Total Operating Cost for 30 Days) 113.800
Total Capital Investment 2,002,200
72
-------
^3 percent of the purchased equipment cost (again based on the "ordinary
chemical plant") the purchased equipment cost was calculated. This
purchased equipment cost would be more in line with what one would expect
for the "ordinary chemical plant" given the above calculated purchased
equipment cost, and the sum of the two is the installed equipment cost
for this particular plant. 2) It is rather doubtful that there should
be any significant difference in the land required for the batch and the
continuous processes. Therefore, the land cost (as a percent of the
purchased equipment cost) was adjusted to give a value of 15,000 to
$20,000.
The fixed capital investment for the ^-stage continuous plant using
0.5 percent sulfuric acid was estimated to be $1,888,000 and the total
capital investment was estimated at $2,002,000.
The estimated manufacturing cost for hydrolyzate sugar using a
wastepaper feed is itemized in Table XIX. An explanation of the various
Items included in this table is given in the text following Table XVI.
The daily operating cost was estimated to be $3,786. The largest single
item in this estimate is the cost of the wastepaper which amounts to 27.5
percent of the manufacturing cost. To determine the cost per pound of
sugar produced, some on stream factor should be assumed since it is
doubtful that the plant will operate at full capacity for 365 days per
year. A factor of 0.9 was chosen and the daily sugar output was then
multiplied by this factor. At full capacity (80 tons dry feed per day)
the plant output is 73,900 pounds of sugar. With an on-stream factor of
0.9 the average daily output of sugar is 66,500 pounds. Theoretically the
on-stream factor should also be applied to the usage of raw materials and
utilities. However, when the reactor system is shut down, the reacting
material is converted all the way to decomposition products and there is
a net lo-ss of raw material over and above the corresponding loss in sugar
production. When the system is restarted, very little sugar will be
obtainable from the material held in the reactor system during shut-down.
Therefore a factor somewhat greater than 0.9 should be applied to raw
materials and utilities depending on the frequency with which shut-downs
will occur. Since the choice of 0.9 is somewhat arbitrary, no on-stream
73
-------
TABLE XIX: ESTIMATED MANUFACTURING COST FOR CONTINUOUS
PROCESS USING A FOUR - STAGE REACTOR SYSTEM
A.
B.
C.
D.
ITEM UNITS/DAY COST
Direct Production Cost
1 . Raw Materials
H SO^ (60 Baume - 77.7%) 4.65 Ton ?26.00/Ton
Limestone (Crushed - 100 Mesh) 4.42 Ton 12.WTon
Wastepaper (Mixed) 80.0 Ton 13.00/Ton
2. Utilities
Electricity 17.600 kw-hr 0.007/kw-hr
Steam (125% of Process Demand) 325,500 # 0.52/1000 #
Process Water 172,000 Gal 0.25/1000 Gal
3. Operating Labor 3 Men/Shift 72 Man-Hrs. 3.00/Man-Hr.
4. Supervisor 1 Man - Day Shift 8 Man-Hrs. 3.50/Man-Hr.
5. Fringe Benefits - 15% Hourly Wage
6. Operating Supplies - 10% of Labor
7. Maintenance and Repairs - 10% F.C.I.
Labor (Per Year) = 5% F.C.I.
Overhead and Supplies (Per Year = 5% F.C.I.
Direct Production Cost
Fixed Charges
1. Depreciation - 12 Year Plant Life - Zero
Salvage Value - 8 1/3% F.C.I. Per Year
2. Local Taxes - 2% FCI Per Year
3. Insurance - 1% FCI Per Year
Fixed Charges
Plant Overhead - 70% of Operating Labor,
Supervision & Maintenance Labor
General Expenses
1. Administrative Costs - 15% of Operating Labor,
Supervision & Maintenance Labor
2. Distribution and Selling Cost - (Not Applicable)
3. Research and Development Cost - 5% Total Prod. Cost.
4. Financing Interest 4% of Total Cap. Investment
Per Year
General Expenses
Total Production Cost (A + B + C + D)
Total Product Cost = ^f^r^ * 5.7$/#Sugar
DAILY COST
$ 121.00
5^.80
1,040.00
123.20
169.20
43.00
216.00
28.00
36.60
21.60
258.00
258.00
2,369.40
426.00
103.50
51.70
581.20
351.50
75.30
190.00
219.00
484.30
3,786.40
74
-------
factor was applied to the raw materials and utilities. Thus the cost per
pound of sugar is determined by dividing the daily cost at full capacity
by nine-tenths times the daily full capacity output. The manufacturing
cost obtained in this way is 5.7 cents per pound of sugar. If one assumed
an on-stream factor of 0.9 and applied it not only to sugar production but
to raw materials and utilities as well, the cost would be 5A5 cents per
pound.
Continuous Process - Optimum number of stages:
Since the reactor system accounts for over seventy percent of the
installed equipment cost the optimization of the plant with respect to
the number of reactor stages is quite important. A four stage system
was assumed as a starting point to get some estimate of the manufacturing
cost. By using some approximations, the total capital investment for a
plant using a three stage reactor can be estimated. Also, the daily
operating cost and the daily sugar production can easily be obtained from
the four stage design. The calculations and assumptions made in revising
the various costs of the four stage system are given in the text following
Table XXI. The revised installed equipment cost is $582,000. Table XX
gives the itemized total capital investment for the continuous process
using a three stage reactor. The fixed capital investment is $1,583,000
compared to $1,888,000 for the four stage process. The estimated
manufacturing cost for the three stage plant is given in Table XXI. The
daily product cost is $3,^66 but the plant capacity, at an on-stream
factor of 0.9, drops from 66,500 to 62,500 pounds per day. Thus, the
manufacturing cost for the three stage plant is 5.55 cents per pound of
sugar as compared to 5.7 cents per pound of sugar for the four stage
process. The four stage process should be compared to the three stage
process to see if the return on the additional investment for another
stage is worthwhile. This comparison is made following Table XXI.
75
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TABLE XX: ESTIMATE OF TOTAL CAPITAL INVESTMENT FOR CONTINUOUS
PROCESS USING A THREE-STAGE REACTOR SYSTEM
1.
2.
3.
k.
5.
6.
7.
8.
9.
10.
11.
12.
ITEM & BASIS OF ESTIMATION
Purchased Equipment - Delivered (P.E.C.)
Equipment Installation (Including Instrumentation
and Insulation) - 43% (P.E.C.)
Installed Equipment Cost
Piping (including Insulation - 36% P.E.C.
Electrical Installations - 15% P.E.C.
Buildings Including Services - 35% P.E.C.
Yard Improvements - 10% P.E.C.
Service Facilities - 35% P.E.C.
Land - 4.8% P.E.C.
Total Physical Plant Cost
Engineering and Construction - 40% PEC
Direct Plant Cost (D.P.C.)
Contractors Fee - 7% D.P.C.
Contingency - 15% D.P.C.
Fixed Capital Investment (F.C.I.)
Working Capital (Total Operating Cost for 30 Days)
Total Capital Investment
COST (CE = 109)
407,000
175,000
582,000
1 if 6, 700
61,000
142,600
40 , 700
142,600
19,500
1,135,100
162,900
1,298,000
90,900
194,600
1,583,500
104,000
1,687,500
76
-------
TABLE XXI: ESTIMATED MANUFACTURING COST FOR CONTINUOUS
PROCESS USING A THREE - STAGE REACTOR SYSTEM
A.
B.
C.
D.
ITEM UNITS/DAY
Direct Production Cost
1 . Raw Materials
H SO^ (60° Baume - 77.7%) 4.02 Tons
Limestone (Crushed - 100 Mesh) 3.78 Tons
Wastepaper (Mixed) 80.0 Tons
2. Utilities
Electricity 15.630 kw-hr.
Steam (125% of Process Demand) 285,500 #
Process Water 172,000 Gal
3. Operating Labor 3 Men/Shift 72 Man-Hrs.
4. Supervisor 1 Man - Day Shift 8 Man-Hrs.
5. Fringe Benefits - 15% Hourly Wage
6. Operating Supplies - 10% of Labor
7. Maintenance and Repairs - 10% F.C.I.
Labor (Per Year) = 5% FCI
Overhead S- Supplies (Per Year) = 5% F.C.I.
Direct Production Cost
Fixed Charges
1. Depreciation - 12 Year Plant Life - Zero
Salvage Value = 8 1/3% FCI per Year
2. Local Taxes - 2% FCI Per Year
3. Insurance - 1% FCI Per Year
Fixed Charges
Plant Overhead - 70% of Operating Labor,
Supervision & Maintenance Labor
General Expenses
1. Administrative Costs - 15% of Operating Labor
Supervision & Maintenance Labor
2. Distribution and Selling Cost (Not Applicable)
3. Research and Development Cost - 5% Product Cost
4. Financing Interest 4% of Total Capital
Investment Per Year
General Expenses
Total Production Cost Excluding Income Tax
t . _ _ _ V
COST DAILY COST
^26.00/Ton 104.60
12. 40 /Ton 46.90
13/Ton 1,040.00
0.007/kw-hr. 109.50
0.52/1000# 148.30
0.25/1000 Gal 43.00
3.00/Man-Hr. 216.00
3.50/Man-Hr. 28.00
36.60
21.60
217.00
217.00
2,228.50
357.00
86.70
43.50
487.20
323.00
69.10
-
173.00
185.00
427.10
3,466.00
(A + B + C + D)
With on-stream factor = 0.9 the daily sugar production is 62,500#
Total Product Cost
$3.466.00 =
62,500#
77
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Modification of Calculations for Three-Stage Reactor System:
Reactor System:
Average cost of one reactor tube = $33,400
Average cost of one screw press = $55,000
Approximate installation cost = $20,000
Savings in equipment cost (installed) = $108,400 (CE=109)
Other Equipment:
By eliminating the 4th reactor, the amount of material that must be
handled by the other equipment (flash tanks, condensers, neutralizer,
centrifuge, and storage tanks) is less. The flow to the 1st flash tank
is decreased by about 14 percent. The equipment could be re-sized for
the smaller flow. However, since this will have only a minor effect on
the total cost, it is assumed here that the size and cost of all other
equipment remains unchanged.
The other equipment that may be eliminated from the process is:
1) Pump number 4 at a cost of $1,600
2) Reactor tube number 4 motor at $1,300
3) Screw Press number 4 motor at $3,400
Utilities:
Electric power usage decreases from 17,600 kw-hr per day for the
four-stage process to 15,630 kw-hr per day for the three-stage process
by eliminating the above three pieces of electrical equipment.
Based on 125 percent of the process demand the steam usage decreases
from 6.78 tons per hour to 5.95 tons per hour. The daily steam usage is
285,000 pounds.
Water usage should remain the same if the final concentration and
losses in centrifugation are to remain the same.
The revised utility costs are:
Electricity - (15,630 kw-hr)($0.007/kw-hr) - $109.50
Steam - (285,500#)($0.52/1000#) - $148.30
78
-------
Raw Materials:
Waste paper requirements remain the same. Sulfuric acid requirements
decrease by 0.0261 tons per hour to a daily usage of 4.02 tons. The
revised sulfuric acid cost is (4. 02) ($26.00) = $104.60.
The limestone must now provide for the neutralization of 0.1444 -
0.0208 = 0.1236 tons/hr of sulfuric acid. Making the same assumptions
as in the previous calculation the required limestone usage is 0.1575 tons
per hour or 3.78 tons per day. The revised limestone cost is (3.78) ($12. 40) =
$46.90.
Sugar Production:
Assuming sugar losses at the centrifuge are the same, the rate of
sugar production with a three-stage reactor system is 1.539 ton/hr - 0.0906
ton/hr = production is 62,500 pounds.
Installed Equipment Cost:
Total saved on installed equipment (CE = 109) =* $115,300 total installed
equipment cost for three reactor system (CE=109) = 697,000 - 115,300 =
$581,700.
Comparison of Thrte-Stage and Four-Stage Reactor Systems:
Three-Stage System:
Basis for profit estimation - 25 percent of total capital investment
per year58' P 75 & ?6 before taxes.
Total capital investment = $1,687,000
Yearly profit (before taxes) - (0.25) ($1 ,687,000) - $422,000
$4-22 000
Profit per pound of product (before taxes) 7olc\ ((.? rnn\ ~ '«^5 cents/
pound sugar
Fictitious selling price -. + ^ "
3 Y #Sugar ffSugar #Sugar
Four-Stage System:
Total capital investment = #2,002,000
Total yearly income at 7.40 cents pound sugar =* ($0.074) (66,500)
(365) - $1,798,000
Total yearly expenses - (3, 786) (365) = $1,382,000
Total yearly profit « $1,798,000 - $1,382,000 = $416,000
79
-------
"six-tenths factor":
F (Capacity of Unit B)1 °'6 (Cost of Unit B)
[(Capacity of Unit A)J = (Cost of Unit A)
In general, most of the log-log plots of costs vs. capacity have a slope
of 0.6. Pump costs were not adjusted since the installed cost for electric
motors varies very little with motor size and the motor cost is usually
a sizeable percentage of the total installed pump cost. The conveyors were
not adjusted either due to the lack of cost data on the small size of
conveyors required.
To maintain a product comparable with the four-stage system and to
eliminate greater sugar losses during centrifugat ion (due to centrifugation
of a more concentrated solution) the hydrolyzate should be diluted before
centrifugation. Therefore the centrifuge will be required to handle about
the same flow rate and its cost should not change significantly.
The following table may be prepared by revising previous calculations.
Item
H-SO, Storage Tank
Limestone Storage Tank
Neutral izer
2 Condensers
2 Flash Tanks
Total Cost
Capacity for
it-Stage React
20,500 Gal.
24,500 Gal.
10,800
100 Ft2 Each
300 Gal. Each
Capacity for
2-Stage React
14,500 Gal.
17,600 Gal.
7,500 Gal.
70 Ft2 Each
200 Gal. Each
Slope
(Ref 10)
0.55
0.51
0.51
0.60
0.53
Cost 4-Stage
CE = 109
26,200
9,200
15,000
9,900
17,900
78,700
Cost 2-Stage
CE = 109
21,700
8,200
12,500
8,000
14,500
64,900
Savings by capacity reduction (Installed, CE109) = 13,800
Other equipment that may be eliminated for the process is:
1) Pump #4 $1,600 (CE = 100)
2) Pump #3 $1,700
3) Reactor tube #4 motor $1,300
4) Reactor tube #3 motor $1,300
5) Screw press #4 motor $3,400
6) Screw press #3 motor $3.500
$12,800 (CE = 100)
80
-------
Comparing Profits:
Three-Stage = $422,000
Four-Stage = $416,000
Therefore the additional investment for the four-stage system should not
be made since there would be a negative return for the additional investment.
The next logical step is to compare a three-stage reactor to a two-stage
reactor to determine if the additional investment for the third stage is
worthwhile. The assumptions and calculations for the various costs of the
two-stage process are given in the text following Table XXII. The installed
equipment cost is found to be $451,000 compared to $582,000 for the three-
stage process. The estimated total capital investment for the two-stage
process is $1,232,000 compared to $1,583,000 for the three-stage process.
Table XXIII lists the various manufacturing costs for the two-stage reactor
sustem. The daily cost is $3,096, but the sugar production has dropped
from 62,500 pounds per day to 52,900 pounds per day so that the manufacturing
cost per pound of sugar increases from 5.55 cents per pound for the three-
stage plant to 5.85 cents per pound. An economic comparison of the
three-stage plant to the two stage plant is noted below. It is seen that
the increase in profit divided by the increase in investment is 36.2
percent. This is above the assumed minimum acceptable return of 25 percent
and therefore places the optimum number of reactor stages at three.
Reactor System:
Average cost of two reactor tubes = 68,600
Average cost of two screw presses = 110,000
Approximate installation cost = 40,000
Savings in reactor system (installed) = 218,600 (CE = 109)
Other Equipment:
By using only the two reactors the flow to the flash tanks is decreased
by 32.5 percent. Therefore some adjustment should be made for smaller
equipment in the rest of the plant. This can be done by the so-called
81
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TABLE XXII: ESTIMATE OF TOTAL CAPITAL INVESTMENT FOR CONTINUOUS
PROCESS USING A TWO - STAGE REACTOR SYSTEM
ITEM & BASIS OF ESTIMATION COST (CE= 109)
1. Purchased Equipment - Delivered (P.E.C.) 315,500
2. Equipment Installation (Including Instrumentation
and Insulation) - If3% P.E.C. 135.500
Installed Equipment Cost ^51,000
3. Piping (Including Insulation) -36% P.E.C. 113,700
k. Electrical Installations - 15% P.E.C. ^7,300
5. Buildings Including Services - 35% P.E.C. 110,500
6. Yard Improvements - 10% P.E.C. 31,500
7. Service Facilities - 35% P.E.C. 110,500
8. Land - 6.18% P.E.C. 19.500
Total Physical Plant Cost 884,000
9. Engineering and Construction - kQ% P.E.C. 126.100
Direct Plant Cost (D.P.C.) 1,010,100
10. Contractors Fee - 7% D.P.C. 70,700
II. Contingency - 15% D.P.C. 151.500
Fixed Capital Investment 1,232,300
12. Working Capital (Total Operating Cost for 30 Days) 92.700
Total Capital Investment 1,325,000
82
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TABLE XXIII: ESTIMATED MANUFACTURING COST FOR CONTINUOUS
PROCESS USING A TWO - STAGE REACTOR SYSTEM
ITEM UNITS/DAY COST DAILY COST
A.
B.
C.
D.
Wi
To
Direct Production Cost
1 . Raw Material s
H2S04 (60° Baume - 77-7%) 3.26 Tons $26.00/Ton
Limestone (Crushed - 100 Mesh) 2.97 Tons 12.40/Ton
Wastepaper (Mixed) 80 Tons 13.00/Ton
2. Utilities
Electricity 13,510 kw-hr 0.007/kw-hr
Steam (125% of Process Demand) 236,000# 0.52/1000#
Process Water 172,000 Gal 0.25/1000 Gal
3. Operating Labor - 3 Men/Shift 72 Man-Hr. 3.00/Man-Hr
4. Supervisor - 1 Man - Day Shift 8 Man-Mrs. 3.50/Man-Hr
5. Fringe Benefits - 15% Hourly Wage
6. Operating Supplies - 10% of Labor
7. Maintenance and Repairs - 10% F.C.I.
Labor (Per Year) = 5% F.C.I.
Overhead & Supplies (Per Year) = 5% F.C.I.
Direct Production Cost
Fixed Charges
1. Depreciation - 12 Year Plant Life - Zero
Salvage Value = 8 1/3% F.C.I. Per Year
2. Local Taxes - 2% FCI Per Year
3. Insurance - 1% F.C.I. Per Year
Fixed Charges
Plant Overhead - 70% of Operating Labor, Supervision
and Maintenance Labor
General Expenses
1. Administrative Costs - 15% of Operating Labor,
Supervision and Maintenance Labor
2. Distribution and Selling Cost - (Not Applicable)
3. Research and Development Cost - 5% Total Product Cost
4. Financing Interest - 4% of Total Capital Investment
Per Year
General Expenses
Total Production Cost
th on-stream factor = 0.9 the daily sugar production is 52,900#
t-i r \ i r -i $3,096.00 .
tal Product Cost - 2 ^Q _ 5.85e/#Sugar
84.70
36.80
1040.00
94.60
122.80
43,00
216.00
28.00
36.60
21.60
169.00
169.00
2062.10
281.50
67.50
33.80
382.80
289.00
62.00
-
155.00
145.00
360.00
3,096.00
83
-------
Savings from eliminated equipment (Installed CE 109) = $13,900
Utilities:
Electric power usage decreases from 17,600 kw-hr in the four-stage
plant to 13,510 kw-hr in the two-stage plant.
Steam usage decreases from 6.78 tons per hour for the four-stage plant
to 4.91 tons per hour in the two-stage plant using 125 percent of process
demand. Daily steam usage Is 236,000 pounds steam.
As mentioned before, water requirements will remain approximately the
same due to dilution prior to centrifugal ion.
The required utility costs are:
Electricity - (13.510 kw-hr) ($0.007/kw-hr) = $94.60
Steam - (236,000 # steam) ($0.52/1000 # st) - $122.80
Raw Materials:
Waste paper usage remains the same. Sulfuric acid requirements decrease
from 4.65 tons per day to 3.26 tons per day for a revised cost of 3.26 x $26.00
=» $84.70.
The limestone must neutralize only 0.097 ton/hr of sulfuric acid compared
to 0.1444 ton/hr with the four-stage plant. Using the same assumptions as
previously the required limestone is 0.1238 tons/hr or a daily usage of 2.97
tons. The revised limestone cost is 2.97 * $12.40 = $36.80.
Sugar Production:
Assuming sugar losses at the centrifuge are the same as for the four-stage
plant the sugar production rate is 1.539 - 0.317 = 1.222 tons/hr. Assuming
an on-stream factor of 0.9 the daily production rate is 52,900 pounds.
Installed Equipment Cost:
Amount saved on reactor system = 218,600
Amount saved on capacity reduction = 13,800
Amount saved by equipment elimination = 13.900
Total saved on two-stage system = $246,300 (CE = 109)
Installed equipment cost for two-stage plant » $697,000 - $246,000 =
$451,000.
84
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Comparison of Two-Stage and Three-Stage Reactor System:
Two-Stage System:
Assume a minimum acceptable return of 25 percent per year before
taxes58 P 75 & 76
Total capital investment - $1,325,000
Yearly profit (before taxes) - (0.25) ($ I ,325,000 - $332,000
Profit per pound of product (before taxes) » /|ic\ \c2 QQQ) " l-72$/# sugar
Total fictitious selling price - +
r # sugar # sugar # sugar
Three-Stage System:
Total capital investment = $1,687,000
Gross yearly income at 7.57$/# ($0.0757) (62, 500#) (365) - $1,729,000
Total yearly expenses - ($3,^66) (365) » $1,266,000
Total yearly profit - $1,729,000 - $1,266,000 = $463,000
Gain in profit - AP - 463,000 - 332,000 » $131,000
Increase in nvestment » A I = 1,687,000 - 1,325,000 » $362,000
AP _ $131.000 _
AI~ $362,000 ~
The annual return on the investment is 36.2 percent which is greater
than 25 percent minimum acceptable return. Therefore, the three-stage
reactor system is the most desirable design from an economic standpoint.
Variation of Costs with Capacity:
Having decided on three reactors for optimum operation of the plant,
the next logical question is: how does the plant size affect product cost.
The largest reactor system produced by The Black Clawson Company could
handle 1,570 tons per day of raw waste material compared to the 80 tons
per day for which this plant is designed. This leaves considerable room
for expansion.
Black Clawson state that the capacity cost exponent for the entire
reactor system is 0.6.
Chilton indicates that, in general, entire plant costs as well as
equipment costs vary according to the "six-tenths factor". Hackney lists
85
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capacity-cost exponents for various processes. Two of the processes are
somewhat similar to the one under consideration here. They are:
Soybean extraction: exponent =0.70
Solvent extraction or treating: exponent « 0.6?
Therefore, although some of the other process equipment (other than the
reactor system) may also be limited to a lower expansion ratio, the maximum
cost exponent of 0.70 was chosen for calculating costs of the larger plants.
This will give a more conservative cost picture than the six-tenths factor.
In Table XXIV, fixed capital investment is given for five different
capacities. Fixed capital investments at larger capacities were obtained by
applying the seven-tenths factor to the 80 ton per day plant and the breakdown
of these larger plants is exactly the same as given in Table XX for the 80
ton per day plant.
TABLE XXIV: Fixed Capital Investment vs Plant Size
CAPACITY
(TONS FEED PER DAY)
80
150
300
500
1000
FIXED CAPITAL INVESTMENT
(CHEM ENG INDEX - 109)
$ 1,583,000
$ 2,460,000
$ 3,990,000
$ 5,720,000
$ 9,260,000
In calculating the manufacturing cost per pound of sugar the following
points should be kept in mind:
1) If the feed to the plant is doubled the usage of all raw
materials is doubled and the production of sugar is also
doubled.
2) If the plant capacity is doubled, water and steam usage will
double, but, due to the fact that larger pumps and larger
motors have higher efficiencies, the electric usage will not
quite double. The assumption that electric usage is proportional
to capacity should, however, be quite adequate for this analysis.
Errors will give conservative results.
3) Operating labor should remain constant as the capacity is
increased based on information obtained from The Black Clawson
Company.
75
86
-------
The itemized operating cost for the three-stage reactor, 80 ton per
day plant is given in Table XXI. Table XXV shows the itemized operating
costs at various capacities.
Comparison of Batch and Continuous Processes:
As is usually the case batch operation is more economical for small
plants than large plants. For the 80 ton per day capacity the manufacturing
cost when operating batch-wise is 5.1 cents per pound of sugar compared to
5.55 cents per pound using a three-stage continuous process. The main
disadvantage in the batch plant is that there is very little advantage to
expansion. As mentioned previously, the 2000 cubic foot digester cannot
be scaled up without making unrealistic demands on the system. Thus to
go to 160 tons per day, one must build essentially two 80 ton per day
plants. Of course certain conservations can be made such as both 80 ton
plants using the same storage tanks and possibly the same centrifuge, but
the capacity-cost exponent should still be close to 1.0. Assuming that it
is 1.0, the economic cross-over from batch to continuous operation takes
place at a plant capacity of 125 tons per day when based on manufacturing
costs.
Variation of Costs with Raw Material Source:
The cost of the raw waste material utilized as feed to the hydrolysis
plant is a significant portion of the total product cost. This factor
increases in significance with increasing plant size. The fraction of
the product cost attributable to raw material for wastepaper
is available from Table XXV and is summarized in Table XXVI.
87
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TABLE XXV: DAILY MANUFACTURING COST FOR CONTINUOUS PLANTS OF
VARIOUS CAPACITIES USING THREE-STAGE REACTOR
Item
A-1 Raw Materials
Limestone
Uastepaper
A-2 Utilities
Electricity
Steam
Process Water
A-3 Operating Labor
A-4 Supervisor
A-5 Fringe Benefits
A-6 Operating Supplies
A-7 Maintenance
Labor
OverheadS-Suppl ies
B-l Depreciation
B-2 Local Taxes
B-3 Insurance
C Plant Overhead
D-l Administrative Cost
D-2 Distribution & Selling Cost
D-3 Research & Development
D-4 Financing Interest
Daily Production Cost
Production Cost Per Pound
80 Ton/Day
Plant
104.60
46.90
1,040.00
190.50
148.30
43.00
216.00
28.00
36.60
21.60
217.00
217.00
357.00
86.70
43.50
323.00
69.10
-
173.00
185.00
3,466.00
5.55
-------
TABLE XXVI: .RAW MATERIAL FRACTION OF PRODUCT COST
Plant Size
(Tons/Day)
80
150
300
500
1000
Product Cost
(Cents/Pound)
5.55
4.91
4.34
4.05
3.65
Waste Feed Fraction
(Percent)
30.0
33.8
38.3
41.0
44.5
The cost ranges for three classes of raw waste materials established
in this report are as follows:
Commodity Price Range
No. 1 mixed paper $4 to 12/Ton
Bagasse $5 to 15/Ton
Organic urban refuse $2.50 to 4.50/Ton Credit
Assuming that the production of sugar per ton of raw feed is about
equal for the three materials and that the materials will be utilized
within fixed metropolitan areas or within a maximum of fifty miles of the
sugar central in the case of bagasse, the above cost figures can be
substituted directly in the manufacturing cost summary. The productivity
assumption seems reasonable based on present knowledge of commodity
compositions as summarized in Tables II and IX.
The direct application of the credit figures for Organic Urban
Refuse may not be realistic in some cases. Since these numbers represent
costs for disposing of mixed refuse (municipal dumping fees) that will in
some cases include non-organic material that can not be used in this process,
such as cans and bottles a preparation charge must be established. In
cases where refractory components can be removed at a profit or zero cost
due to the existence of a salvage market, a charge for preparation of the
waste will not apply. Inclusion of a preparation step will result in a
fourth alternative in the waste commodity list and will be a function of
the local municipal waste collection system.
89
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One method of preparation of mixed urban refuse is the inclusion of
a hydropulping operation as a prehydrolysis step. This approach is
detailed in the discussion following Table XXVII. The costs of the
hydropulping operation vary with plant size and therefore cannot be expressed
as a single raw material cost function. Hydropulping costs vary from $39**
per day for the 80 ton day continuous plant to $1581 per day for the 1000
ton per day plant. This results in an actual charge to the hydrolysis
operation of $2.42 per ton for the Mixed Urban Refuse at the lower dumping
fee of $2.50 per ton and on 80 ton per day plant, and a credit to the
hydrolysis step of $2.92 per ton for the $4.50 per ton dumping fee at the
1000 ton per day plant. Dumping fee credits balance the additional
preparation costs for hydropulping at about the 300 ton per day plant size
the $2.50 per ton fee and the 80 ton per day plant for the $4.50 per ton
fee.
The variation in product cost in cents per pound of sugar with plant
size and raw material are shown graphically in Figure 16. The shaded area.
represents the cost range expected in each instance. The cost ranges by
waste commodity is summarized below:
Cost Range
Commodity Cents/Pound Sugar
No. 1 Mixed Paper 2.59 - 5.42
Bagasse 2.73 - 5.81
Organic Urban Refuse 1.51 - 3.56
Mixed Urban Refuse 1.71 - 4.19
The highest costs are always represented by the smallest plant size
and the high end of the commodity price range. The converse is true for
the low costs.
90
-------
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-------
TABLE XXVII: PRODUCTION COST IN CENTS PER POUND OF SUGAR FOR VARIOUS RAW WASTE
COMMODITIES AND VARIOUS PLANT CAPACITIES
(BASIS: THREE STAGE CONTINUOUS PLANT)
RAW MATERIALS
PLANT CAPACITIES
T Price 80 Ton/Day
lype ' $/Ton Plant
No. 1
Mixed Wastepaper 4.00
12.00
Bagasse 5.00
15.00
Organ
Mixed
*
ic Urban Refuse 2.50 Cr.
4.50 Cr.
Urban Refuse " 2.50 Cr.
4.50 Cr.
4.39
5.42
4.53
5.81
3.56
3.30
4J9
3.94
150 Ton/Day 300 Ton/Day 500 Ton/Day 1000 Ton/Day
Plant Plant Plant Plant
3.76
4.80
3.90
5.18
2.93
2.68
3.39
3.13
3.20
4,22
3.33
4.60
2.36
2.11
2.69
2.44
2.91
3.93
3.03
4.32
2.07
1.81
2.34
2.08
2.59
3.62
2.73
4.01
1.76
1.51
1.96
1.71
Includes hydropulper operation
Cost of Adding Hydropulping Preparation Step:
Capital equipment costs for an 80 ton per day plant were estimated
by The Black Clawson Company, Middletown, Ohio, as $75,000 to $100,000.
Since this operation can be performed in mild steel the lower range of
$75,000 plus $5,000 for necessary auxilliaries is chosen and the following
analysis made:
ITEM & BASIS OF ESTIMATE
1. Purchased Equipment - Delivered (P.E.G.)
2. Equipment Installation (Including Instrumentation
and Insulation) = 43% P.E.C.
Installed Equipment Cost
3. Piping (Including Insulation) 36% P.E.C.
4. Electrical Installations 15% P.E.C.
5. Buildings Including Services - 35% P.E.C.
6. Yard Improvements - 10% P.E.C.
7. Service Facilities - 35% P.E.C.
COST (C.E.=109)
80,000
34*400
114,400
28,800
12,000
28,000
8,000
28,000
92
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ITEM & BASIS OF ESTIMATE (Continued) COST (C.E.-109)
8. Land - 6% P.E.C. 4.800
Total Physical Plant Cost 224,000
9. Engineering and Construction 40% P.E.C. 32.000
Direct Plant Cost (D.P.C.) 256,000
10. Contractors Fee 7% D.P.C. 17,900
11. Contingency 10% D.P.C. 25.600
Fixed Capital Investment (F.C.I.) 229,500
A. Fixed Charges Due to Addition of Hydropulper:
Daily Cost
I. Depreciation - 12 year plant life - zero salvage
Value = 8-1/3% F.C.I, per year 68.50
2. Local Taxes - 2% F.C.I, per year 16.40
3. Insurance - 1% F.C.I, per year 8.20
Fixed Charges $93.10
Note: A scale-up factor of 0.7 was used in calculating the larger plants.
B. Additional Direct Production Costs:
1. Operating labor 1 man/shift 24 man hrs. (?) $3.00 72.00
2. Fringe Benefits - 15% of operating labor 10.80
3. Operating Supplies - 10% of labor 7.20
4. Maintenance & Repairs - 10% F.C.I, per year 82.00
Direct Production Cost $172.00
C. Overhead and G & A
I. Additional overhead - 70% direct & maintenance
labor = 0.70 x 113 79.00
2. Administrative costs - 15% direct & maintenance
labor = 0.15 x 113 16.90
3. Financing interest = 4% F.C.I, per year 32.80
$128.70
Total Daily Production Cost due to Hydropulper
addition. A + B + C = $393.80
93
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The Daily Production Cost due to Hydropulper Addition for Other Plant
Sizes is as Follows:
Plant Size Daily Cost
80 $394
150 $531
300 $768
500 $1038
1000 $1581
Typical Calculation for Sugar Production Costs using Mixed Urban Refuse:
Daily production cost 80 ton/day plant (from Table XXV) = 3,466.00
Additional Cost due to hydropulper 39*1.00
Total Cost 3,860.00
Subtract wastepaper raw material cost (Table XXV) 1.040,00
2,820.00
Apply mixed refuse dumping fee credit ($4.50/ton) 360.00
Daily Production Cost 2,460.00
Daily Production = 62,500 pounds sugar.
Production Cost per pound sugar = $2,460.00/62,500 » 3.94
-------
E. COMMENTS AND CONCLUSIONS:
The design of a chemical processing plant based on data not specific
to the proposed process is always a questionable approach. Sincere attempts
were made in all judgements to justify the necessary assumptions required
for plant design and as a result a detailed design effort was made for the
hydrolysis plant.
The desireabi1ity of the batch reactor plant is questioned due to
problems in process control such as porous bed channeling and the attendant
variations in raw material utilization, product decomposition and pressure-
temperature compensations needed. The Springfield, Oregon plant using
digesters of the size proposed in this report was never able to operate at
full capacity due to trouble in the digester.
The continuous process approach is logical from both technical and
economic considerations. Reductions in product decomposition and better
overall process controls due to stage-wise segregation should result in an
operation that is capable of close control. Then too, the large plants that
have economic potential will require the use of the continuous process.
The economic considerations for this plant have been consistently
biased to the conservative side in order to compensate for unknown problems
that may exist by converting the process kinetics from wood waste to other
cellulosic raw materials. This approach may be excessive in this case
since there is some consensus that the waste materials considered as
feedstock for this plant will be easier or at least as easy to hydrolyze
as wood waste. However, without this specific knowledge the conservative
approach to design economics was felt to be justified.
The final verification of the process assumptions must, of course,
be made in the laboratory.
95
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THE FERMENTATION PROCESS
A. Introduction
UNDERKOFFLERAND MICKEY53 introduce the fermentation industries as
"the branch of chemical manufacture which yields useful products through
the vital activities of microorganisms. Fermentation, in the broad
sense in which the term is now generally used, may be defined as a
metabolic process in which chemical changes are brought about in an
organic substrate through the activities of enzymes secreted by micro-
organisms."
Two general processes of fermentation are practiced today: 1) The
anaerobic process in which atmospheric oxygen is not involved and is
represented by the alcohol producers including the wine and beer manu-
facturers, and 2) the aerobic process in which large quantities of
atmospheric oxygen are consumed for the purpose of production of cell
materials for example in the production of yeasts. The latter category is
of primary interest in this study.
Yeast propogation can take place on many diverse sugar containing
substrates. In the case of the hydrolysis sugars, both hexose and pentose
types are present in quant ity. Therefore, i t is desirable to select a micro-
organism that can utilize both species. One such microorganism is the
yeast Candida utilis commonly called Torula. This species was developed
for use in plant scale equipment in Germany and has been used extensively
as a food and animal feed yeast. Torula exhibits rapid growth rates and
has other properties of acid tolerance and the assimilation of inorganic
nitrogen that make it useful for consideration in the fermentation of
hydrolyzate sugars.
Process equipment design, yeast culture maintenance, contamination
problems and product handling systems are all serious considerations
of a yeast plant. When continuous cultures are to be maintained, special
effort in equipment design and "housekeeping" measures are required.
Although some of the latter can be controlled by chemical and thermal
conditions conducive to the microorganism of interest, the specificity
of process parameters is not an exact science and the threat of contamina-
tion and loss exists. Pilot studies of organisms and operating conditions
are always recommended.
96
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B. PROCESS CONSIDERATIONS:
The fermentation process in this instance consists of the propoga-
tion and recovery of a microorganism. Briefly, this is carried out by
growing a yeast on the sugar solution resulting from the hydrolysis
steps. In addition to sugars, other nutrients required include a nitrogen
source, oxygen, small amounts of phosphate, and other minerals in even
smaller amounts. Growth is carried out at temperatures in the range
of 20 to 35 C in reactors provided with a means of agitation. This may
be a stirrer of various types, or may simply be the introduction of
large amounts of air into the fermentor through perforated pipes at the
bottom of the vessel.
When the yeast cell concentration is adequate, the broth and sus-
pended cells may be harvested by passage through a centrifuge which
since the cells have a density slightly greater than that of the broth
and a size of approximately five microns, read?ly removes them. If the
fermentor is operated continuously, a constant feed of fresh medium is
pumped into the vessel, while a stream of broth and cells goes to the
centrifuge. After centrifugation, the cells may be washed and dried,
or may be dried directly.
Nature of the Organism:
The organism which is best suited to the overall process is the yeast
Candida utilis. This organism, known also as Torula utilis, has been
widely used for production of food and fodder yeast from sulfite liquor
and wood hydrolyzates because it has the ability to assimilate a wide
variety of carbon sources, particularly the pentoses which comprise an
important fraction of the available sugar. Common baker's yeast, which
is also a good food and fodder yeast, is unable to assimilate pentoses,
and would 'therefore be unsuitable for the proposed process.
The protsin content of the yeast is approximately 50 per cent
based on dry weight. In addition yeast is a significant source of'B complex
vi tami ns.
While it would be possible to use bacteria as a source of single-
cell protein, in this particular application Candida utilis yeast is
to be preferred because of its known value as a source of protein for
animal feeding, its frequent usage as a vitamin source in human foods,
97
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and the fact that since it is larger than bacterial cells the costs of
centrifugation will be lower than if bacteria were being used. It is
well-suited to the substrate available, and hence no advantage is to be expected
from using bacteria in this particular application.
Nutrients Required:
The basic feedstock (product of the continuous hydrolysis process)
consists of 24.92 tons of solution per hour containing 1.3^+0 tons of
glucose and 0.199 tons of xylose, and hence has a sugar concentration
of 6.17 per cent. In order to calculate the other nutrients required,
the information needed is:
a. composition of cells
b. yield based on sugars
c. yield based on oxygen
jQ
Typical yeast cells analyze as follows : Carbon, kk.6 per cent;
nitrogen, 8.5 per cent; phosphorous, 1.1 per cent; potassium, 2.2 per
cent; and sulfur, 0.6 per cent. A yield of dry cell mass of 50 per cent
based on sugar consumed will be used; this will vary from kS to 55 per cent
79
depending on operating conditions which must be determined experimentally.
An oxygen requirement of 1.05 pounds of oxygen per pound of dry cell
78
mass is a typical oxygen requirement for a well operated process and
will be used for purposes of calculation.
Hence, the rate of dry yeast production per hour must be (1.539)(0.5) =
0.77 tons of 15^0 pounds dry yeast per hour. This will require the
consumption of the following chemicals in pounds per hour:
Ammonia (.085) 05^0) (17/1*0 = 159
Phosphoric Acid (.011)(15^0)(98/31) =52.5
Potassium Chloride (.022)(15^0)(7^.5/39) = 6^.6
Oxygen (1.05)(15^0) = 1615
The requirement for sulfur will be met either from the addition
of potassium sulfate, if that proves the cheapest form of potassium,
or by the dissolved calcium sulfate present in the feedstock. The
potassium may also be added as the hydroxide if It is necessary to raise
the pH of the feedstock to the region of pH 3 to 5 required for growth
of this organism. Addition of small amounts of magnesium and iron may
98
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be needed if there is insufficient present in the limestone or water,
but these represent insignificant costs, and will be neglected here.
Productivity:
The productivity of the fermentor system will be limited by the
rate of oxygen transfer from the air to the fermentation broth. Industrial
experience with yeast production indicates that a rate of 120 millimoles
of oxygen absorbed per liter-hour is an economic rate, in terms of power
79
consumption. This rate of oxygen transfer corresponds to 3.8^ grams of
oxygen per liter-hour or (3.84)(100/105)=3.66 grams of yeast per liter-
hour.
The productivity is equal to the product of the cell concentration
times the dilution rate, where dilution rate is defined as the ratio of
media feed rate to fermentor volume. Thus, (dilution rate)(cell concentra-
tion) = 3.66 grams per liter-hour. The maximum cell concentration would
be attained with undiluted feedstock, and would be 30.85 grams per liter.
For this concentration of cells, the dilution rate would be (3.66/
30.85) = 0.118 hr"1.
If it were desired to operate with a somewhat more dilute solution,
as is sometimes the case, the feedstock could be diluted to yield a
concentration of sugars of k per cent and a yeast concentration of
20 grams per liter. At this concentration, the maximum dilution rate
I _]
for the accepted productivity would be (3.66/20) = 0.183 hr . The
effect of this dilution will be considered later under centrifuge
calculations, where it will be seen that the major effect will be to
require somewhat greater centrifuge capacity.
The fermentation volume required during steady-state continuous
operation is (15^0)(k$k)/(3.66) = 190,000 liters of actual liquid
volume. To provide for an expansion of volume because of gassing with
air and to provide some freeboard for foaming, this will be increased
by 200 per cent, so that the nominal fermentation capacity must be
570,000 liters.
Fermentor:
The fermentor will be essentially a cylinder whose ratio of
height to diameter is 3 to 1. This is not a very important variable,
and satisfactory fermentors can be had with height to diameter ratios
varying from 1 to 1 to k to 1. The bottom will be standard dished, and
99
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the approximate dimensions to hold 370,000 liters will be 20.6 feet in
diameter and 62 feet in height. The material of construction will be
carbon steel. The possibility of using wood is considered as an economic
alternate in Case 2 presented in Tables XXXII through XXXV.
While the use of wood fermentors is not "modern", it is believed
to be a reasonable approach because the fermentation can be carried out
at low pH making asepsis unnecessary. Furthermore, at a low pH no
pathogens can develop, so that there will be no hazard because of the
inability to sterilize. The wood can be painted with epoxy paint
making sanitizing convenient. It would be desirable to evaluate on a
small scale first, the use of epoxy-painted redwood or cypress
fermentors to see what maintenance problems develop. If it should be
possible to use them, and this is a good probability, the savings in
capital costs are substantial.
Air Requirements:
While the stoichiometric amount of oxygen required was calculated
to be 1615 pounds per hour, usual experience in yeast production '
indicates that the efficiency of oxygen absorbtion is typically only
15 per cent. Thus, the amount of air required is (1615)(.15) (.21) =
51,200 pounds per hour, or at 68°F and 1 atm 690,000 cubic feet of air
per hour.
This quantity of air must be supplied at a higher pressure to
provide for the hydrostatic head in the fermentor, pressure drop through
the lines, and pressure drop through the perforations. The hydrostatic
head contributes 10.3 psig and the other pressure drops are estimated
to be approximately 10 psig. Therefore, the air supply should be at a
pressure of 20 psig.
In this application, the agitation will be entirely in the form of
air dispersed from tubes at the bottom of the fermentor. Frequently,
Waldhof-type fermentors are used in which a considerable fraction of
the power is supplied by an agitator. However, the capital costs are
considerably higher and the electric power costs are only slightly lower.
Mixer type fermentors are often used in Europe, while in this country
many fermentors of the air-agitated type are used. The total operating
costs are not greatly different, and it is suggested that an air-
agitated type be used in this application.
100
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Heat Production and Cooling:
As a result of fermentation, the heat production is estimated to
/- -jO
be 15.6 x 10 BTU per ton of yeast produced. For this process,
therefore, (15.6x10 ) (15W2000) = 12 x 10 BTU per hour must be removed
from the fermentor. In order to do this, fermentation broth at 90 F
will be pumped to an external refrigeration system, and will be returned
to the fermentor at 85 F. This slight drop in temperature will not
affect the growth of the organisms.
The external refrigeration system in turn will be cooled by water
from a cooling tower.
As the accompanying comparisons for Case 1 and Case 2 show, if the
fermentation plant can be located in a part of the country in which cool
surface water(pelow 65 to 70 F) is available, a very large savings is
possible because mechanical refrigeration and a cooling tower is not
required. Such locations, using for instance sea water, might be:
Boston, Seattle, San Francisco, or New York; cool fresh water might be
available on a year round basis at Chicago, Detroit or Minneapolis.
Cell Recovery:
The yeast concentration in the effluent from the fermentor will
be either 20 or 30.85 grams of dry solid per liter of solution. In
order to obtain a dried product, initial concentration of the effluent
stream is necessary. There are several methods which, in theory, are
applicable in concentrating solid suspensions. These are gravitational
settling, filtration and centrifugation. A brief summary is presented
below to show the rationale in the selection of the method of concentra-
tion.
81
Yeast cells such as Candida utilis are approximately 3.5 by 7 microns
and other species such as Saccharomyces cerevisiae have mean diameters
Oo
of approximately 5.5 microns. The density of yeast (S. cerevisiae)
On
in aqueous solution is approximately 1.08 gram per cubic centimeter.
Suspensions of yeast will settle according to the modified Stoke's law
for hindered settling:
101
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r~J
L 1 +
where:
U = hindered settling velocity
nr = constant
c = volume fraction of solids
g = gravitational constant
C
d = diameter of particle
/) = density of particle
n = density of liquid
H - viscosity of liquid
It is therefore possible to use gravitational settling tanks to
concentrate suspensions such as yeast. However, the settling area
required is quite large and renders this unpractical. For example,
using a mean particle diameter of 6 microns, the hindered settling
velocity is calculated to be on the order of 1,1x10 centimeters per
second. At this rate, the settling area required for the production of
15^0 pounds of yeast per hour is approximately 15,000 square meters.
Alternatively, filtration is possible as a method of recovery
provided that the resistance of the yeast cake during filtration is low
enough so that a sufficient rate can be achieved. This method, however,
has not been successful on an industrial scale due to the nature of the
cake formed during filtration. It has been found that the yeast cake
"binds" easily and the rate of filtration becomes exceedingly small
Q'J
and thus renders this approach unpractical.
In view of these facts, the method most commonly used for the
recovery of yeast on an industrial scale is by the centrifugal
OK Qr
separator. ' The throughput of a centrifugal separator can be shown
to be expressed in the following equation:
102
-------
Kdp2 (n° -
S
e
where:
Q. = Flow rate through centrifuge
K = constant
d = diameter of the particle
P
n = density of the particle
P
n. = density of the liquid
r = equivalent diameter of the centrifuge
w = rotational speed of the centrifuge
jU = viscosity of the liquid
V = volume holdup of the liquid in centrifuge
S « equivalent sedimentation distance of the particle
It can be seen from equation 2 that one reason for selecting yeasts
instead of other unicellular organisms such as bacteria as a product
is the relative ease of recovery of the yeast. Theory predicts the
throughput of a centrifuge is proportional to the square of the
particle diameter. In this case to separate a yeast having a mean
diameter of 6 microns in comparison to a bacterium of 1.5 micron, the
centrifuge throughput for the yeast is nearly sixteen times greater
than that for the bacterium. Considering necessary capital investment
costs as well as operating costs, the selection of yeast as the organism
has a positive economic basis.
It is envisioned that the yeast from the fermentor is fed directly
to continuous sludge discharge type of centrifuges. This type of
machine is commercially available and has been used successfully in
O-J OK Q/: Q-j
industrial yeast production. ' ' ' A battery of three 6000 gallons
per hour, 20 horsepower continuous sludge discharge separators will be
required. Yeast from the fermentor will be concentrated from approximately
two hundred grams per liter after one pass through the centrifuge. It
will be necessary to wash the concentrated paste to remove undesirable
tastes and odor. Counter-current washing using in-line mixers is
103
-------
proposed in order to minimize the water consumption. This procedure
is commonly employed in the industrial yeast manufacturing. The
effluents from the first and second stage centrifugation can be recycled
to the hydrolyzer for reuse. The solid paste from the last centrifuge
is refrigerated to prevent contamination and pumped to the drum dryer.
The solids from the last centfifugation stage will have undergone an
approximate ten fold concentration factor and will contain approximately
twenty percent dry solids.
Drying:
The concentrated paste from the third centrifuge will be dried by
means of a double drum atmospheric dryer. It has been shown by Inskeep
86
et al that yeast grown on sulfite waste liquor can be drum dried
using 85 psig steam to produce a non-viable product of adequate nutri-
tional value for animal feed supplements. In addition, drum dryers
require a lower capital investment as well as lower operating and
maintenance costs per pound of water removed. The moisture content of
the feed to the drum dryer will range from 80 to 85 percent. For the
production of 15^ pounds of dry yeast per hour, the drum dryer must
evaporate 12,350 pounds of water per hour. A representative average
product rate for a double drum dryer was reported by Perry to be on
the order of 3.5 pounds of product per hour per square foot of drum
surface. Therefore a drum dryer having approximately kkO square feet
of drying area will be required. The product from the dryer will
contain 2 to 10 per cent moisture.
After drying, the lumpy product will be processed through a
hammer mill, be screened and finally pass into a storage hopper capable
of holding one day's production. The product in the hopper will dis-
charge to a chute permitting bags or drums to be filled for shipment.
C. Economic Analysis
The flow sheet for the fermentation process is shown in Figure 17.
The required process equipment together with materials of construction
and costs are noted in Tables XXVIII and XXXII for two alternate plant
designs. Costs indicated for various items of equipment are taken from
88
Bauman.
-------
CENTRIFUGE
M
-------
Two plant conditions are displayed and developed as: Case 1, the
maximum cost plant, and Case 2, the minimum cost plant. The major
economics reflected in Case 2 are the substitution of a fermentor of
wooden construction for the metal construction indicated in Case 1,
and the use of a local surface water source for cooling in place of
the refrigeration-cooling tower system proposed in Case 1.
The substitution of wood for metal fermentors is not unusual and
had, for many years, been the principal material of construction in
many segments of the fermentation industries. Economics attributed to
this factor equal $125,000 of the purchased equipment cost. This
represents a cost reduction of about 0.5 cents per pound of yeast for
the 80 ton per day plant, or expressed in another way it equals a 5
per cent reduction in product costs. This economy should be universally
applicable to plants at any location.
The second economy, that of using a large body of surface water
for cooling purposes, is more specific in its application. A local
large body of cooling water must be present that is available for use
to the fermentation plant. Although the opportunity to apply this cost
reduction scheme is limited, it is nonetheless very attractive where
it can be utilized. Product cost reductions of 2.76 cents per pound
or 30 per cent can be realized by employing this method of cooling.
Coastal municipalities and perhaps some locations on the Great Lakes
appear to have the best opportunity to apply this cost saving factor.
Case 1 data is presented in Tables XXVIII through XXXI. Plant
cost figures developed in Tables XXVIII to XXX are based on the 80 ton
per day of wastepaper to the hydrolysis operations. Table XXXI expands
the plant in increments to the 1000 ton per day size.
Case 2 data is presented in Tables XXXII through XXXV. Tables
XXXII to XXXIV refer to the 80 ton per day plant while Table XXXV
compares cost factors for the 80 and 500 ton per day plants.
Table XXXVI summarizes yeast product costs in cents per pound
for cases 1 and 2 as a function of plant size.
106
-------
TABLE XXVIII: EQUIPMENT COSTS FOR FERMENTATION SYSTEM
CASE I
150
Item
Size
Material of Construction
Purchased
Cost
Nu^rjent .Makeup
Metering Pumps
Hydrolyzate pump
Ammonia metering equip.
Air Supply
Air Compressor
Fermentor
Cool ing
Refrigeration System
Broth circulation pump
Cool ing Tower
Recovery and Washing
Centrifuges, continuous
Pumps
Drying and Packaging
Dryers-Double Drum
Hammer Mill
Storage
Packaging System
50 GPH
100 GPM
11,500 CFM
570,000 Liters
1000 tons
k2 HP
17xl06Btu/hr
100-150 GPM
100 GPM
12,UOO#/hr
1 Ton/hr
20 Tons
I ron
Cast Iron-Centrifugal
I ron
Iron-Centrifugal
I ron
Iron-Centr ifugal
Cast Iron-Centrifugal
Aluminum
Total Equipment Cost
1,200
1 ,000
800
126,000
1^5,000
155,000
2,000
80,000
5^,000
3,000
86,000
10,000
15,000
5.000
$684,000
107
-------
TABLE XXIX: ESTIMATE OF TOTAL CAPITAL INVESTMENT:FERMENTATION PLANT
CASE 1
Item and Basis for Estimation Cost
1. Purchased equipment-delivered (P.E.C.) 684,000
2. Equipment installation (including instrumentation) 43% P.E.C. 294tOOP
Installed equipment cost 978,000
3. Piping (Including insulation) - 27% P.E.C. 184,000
4. Electrical installations - 15% P.E.C. 105,000
5. Buildings, (including services)- 35% P.E.C. 239,000
6. Yard improvements - 10% P.E.C. 68,000
7. Service facilities - 35% P.E.C. 239,000
8. Land - 4.8% P.E.C. 33.000
Total physical plant cost 1,846,000
9. Engineering and construction - 40% P.E.C. 274rOOP
Direct plant cost (D.P.C.) 2,120,000
10. Contractors fee - 7% D.P.C. 148,000
11. Contingency - 15% D.P.C. 318.OOP
Fixed capital investment (F.C.I.) 2,586,PPP
12. Working capital (total operating cost for 30 days) 102rOOP
Total capital investment 2,688,000
108
-------
TABLE XXX: ESTIMATED MANUFACTURING COST^FERMENTATION PROCESS
CASE 1
Item Units/day Cost Daily Cost
A.
Direct production cost
1. Raw Materials (excluding cost of
Ammonia, anhydrous
Phosphoric acid, 53%
Potassium chloride, 95~99%
sugar)
1.91 tons
1. 19 tons
0.78 tons
$92.00/ton
51.00/ton
30.00/ton
175.80
60.60
23.40
2. Utilities
Electricity 42,700 kw-hr 0.007/kw-hr 299.00
Steam 360,000 # 0.52/1000# 187.30
Process water 221,000 gal. 0.25/1000 gal 55.20
3. Operating labor 2 men/shift 48 man-hrs 3.00/man-hr 144.00
4. Supervisor (Use Hydrolysis Plant Supervisor)
5. Fringe benefits 15% hourly wage 21.60
6. Operating supplies 10% of labor 14.40
7. Maintenance & Repairs 10% FCI/yr. 719.00
Direct Production Cost 1,700,30
B. Fixed Charges
1. Depreciation - 12 yr. plant life zero salvage
value, = 8-1/3% FCI/yr 600.00
2. Local Taxes - 2% FCI/yr 144.00
3. Insurance - 1% FCI/yr 72.00
Fixed Charges 816.00
C. Plant Overhead - 70% operating labor, supervision
and maintenance labor 352.00
D. General Expenses
1. Administrative 15% of operating labor, supervision and
maintenance labor 75.50
2. Distribution and selling cost (not applicable)
3. Research and development 5% product cost 170.00
4. Interest 4% TCI/yr 299.00
General expenses 544.50
Total production cost 3,412.80
Production Cost/If Yeast = $0.092/# (excluding cost of sugar)
109
-------
TABLE XXXI: DAILY MANUFACTURING COST FOR YEAST AT VARIOUS PLANT CAPACITIES
CASE 1
1 tern
Fixed Capital Investment
A-l Raw Materials
A-2 Util ities
A-3 Operating Labor
A-4 Supervi sor
A-5 Fringe Benefits
A-6 Operating Supplies
A-? Maintenance & Repairs
B-l Depreciation
B-2 Local Taxes
B-3 Insurance
C Overhead
D-l Administrative
D-2 Dist.&Sell ing
D-3 R&D
D-4 Interest
Daily Prodn.Cost
Prodn./day (#/day)
Prodn.cost/# Yeast
(Excluding cost of sugar)
80 Ton /day
2,586,000
259.80
531.50
144.00
-
21.60
14.40
719.00
600.00
144.00
72.00
352.00
75.50
-
170.00
299.00
3,412.80
37,000
9.22$/#
150
4,005^,000
487.00
995 .00
144.00
-
21.60
14.40
1,114.00
930.00
223.00
111.50
491 .00
1 05 . 30
-
293.00
465.00
5,395.00
69,400
7.78$/#
300
6,515,000
974.00
1,990.00
144.00
-
21.60
14.40
1,810.00
1,510.00
362.00
181.50
734.00
157.20
-
500.00
754.00
9,153.00
138,500
6.60«/#
500
9., 050, 000
1 ,558.00
3,180.00
144.00
-
21.60
14.40
2,520.00
2,100.00
504.00
252.00
984.00
211.00
-
660.00
1,050.00
13,200.00
231,500
5.70c/#
1000
14,740,000
3,116.00
6,360.00
144.00
-
21.60
14.40
4,100.00
3,420.00
820.00
420.00
1,535.00
329.00
-
1,160.00
1,715.00
23,155.00
463,000
5.00
-------
TABLE XXXII: EQUIPMENT COSTS FOR FERMENTATION SYSTEM
CASE 2
Item
Nutrient Makeup
Air Compressor
Fermentor
Size Material of Construction
(See Table XVII!)
570,000 liters Redwood or Fir
Purchase
Price
3,000
126,000
30,000
Cool ing
Broth circulation pumps k2 HP Iron-centrifugal 2,000
Heat exchangers 6000ft Admiralty Brass 52,000
Recovery and Washing (See Table XVI11) 57,000
Drying and Packaging (See Table XVIII) 116.000
Total Equipment Cost $386,000
11
-------
TABLE XXXIII: ESTIMATE OF TOTAL CAPITAL INVESTMENT'.FERMENT AT I ON PLANT
CASE 2
I. Purchased equipment-delivered (P.E.G.) 386,000
2. Equipment installation (including instrumentation) ,/-, nnn
k3% P-.E.C. 163.000
Installed Equipment Cost 5^3,000
3. Piping (Including insulation) - 27% P.E.C. 103,000
k. Electrical Installations - 15% P.E.C. 57,000
5. Buildings (Including Services) - 35% P.E.C. 133,000
6. Yard Improvements - 10% P.E.C. 38,000
7. Service Facilities - 35% P.E.C. 133,000
8. Land - 4.8% P.E.C. 18.000
Total Physical Plant Cost 1,025,000
9. Engineering and Construction - kO% P.E.C. 152.000
Direct Plant Cost 1,177,000
10. Contractors Fee - 7% D.P.C. 82,000
11. Contingency - 15% D.P.C. 176.000
Fixed Capital Investment 1,^35,000
12. Working Capital 66.500
Total Capital Investment 1,501,500
112
-------
TABLE XXXIV: ESTIMATED MANUFACTURING COST'FERMENTATION PROCESS
CASE 2
Item
Units/Day
Cost
Dally Cost
A. Direct production cost
i. Raw materials (excluding cost of sugar)
Ammonia, anhydrous
Phosphoric aicd, 53%
Potassium Chloride, 95-99%
2. Utilities
Electricity 18,300 kw-hr
Steam (125% of demand) 360,000#
Process water 144,000 gal
1.91 tons
1.19 tons
0.78 tons
$92.00/ton
51 .00/ton
30.00/ton
175.80
60.60
23.40
0.007/kw/hr 128.00
0.52/1000# 187.30
0.25/1000 gal. 36.00
3. Operating labor 2 men/shift 48 man-hrs
4. Supervisor (Use Hytircflysis Plant Supervisor)
5. Fringe benefits 15% hourly wage
6. Operating supplies 10% of labor
7. Maintenance & Repairs, 10% FCJ/yr
Direct Production Cost
B. Fixed Charges
1. Depreciation, 8-1/3% FCI/yr
2. Local Taxes 2% FC l/yr
3. Insurance 1% FCI/yr
Fixed Charges
C. Plant overhead, 70% of operating labor, supervision,
and maintenance labor
D. General Expenses
1. Administrative 15% of oper.labor, super, & Ma int. Labor
2. Distrib & Sell ing
3. R & D 5% Product Cost
4. Interest, 4% TCI/yr
General Expenses
Total Production cost
144.00
21.60
14.40
398.00
1,189.10
240.00
51.40
107.00
168.00
326.40
2,208.50
Production Cost/#Yeast = $0.0596/# (excluding cost of sugar)
113
-------
TABLE XXXV: DAILY MANUFACTURING COST FOR YEAST AT VARIOUS PLANT CAPACITIES
CASE 2
Item
(FCI)
A-l Raw Materials
A-2 Utilities
A-3 Operating Labor
A-4 Supervisor
A-5 Fringe Benefits
A-6 Operating Supplies
A-7 Maintenance & Repairs
B-l Depreciation
B-2 Local Taxes
B-3 Insurance
C Overhead
D-l Administrative
D-2 Dist. & Selling
D-3 R & D
D-4 Interest
Daily Prodn. Cost
Prodn/Day
Prodn cost/#Yeast
(Excluding Cost of Sugar)
80 Ton/Day
1,435,000
259.80
451.30
144.00
-
21.60
14.40
398.00
333.00
80.00
40.00
240.00
51.40
-
107.00
168.00
2,208.50
37,000
5.96e/#
500
5,020,000
1,622.00
2,620.00
144.00
-
21.60
14.40
1,392.00
1,165.00
280.00
140.00
588.00
126.00
-
458.00
588.00
9,159.00
231,500
3.96<:/#
114
-------
TABLE XXXVI: YEAST PRODUCT COSTS VS. PLANT SIZE
.*
(Basis:
Plant Size
feed to hydrolysis plant)
80 Ton/Day
150
300
500
1000
Product Cost
Case 1
9.22
7.78
6.60
5.70
5.00
for Yeast - Cents/pound
Case 2
5.96
3.96
* Note: These figures do not include the cost of the hydrolyzate
sugars.
For Case 1 using wood fermentors the product cost for an 80 ton per
day plant is 8.72 cents per pound, excluding the cost of hydrolyzate sugar.
D. Comments and Conclusions
Fermentation plant design and location are of great importance in
minimizing product costs. Power and cooling water utilization factors
are a prime consideration in plant operating costs and certainly make the
choice of plant location on or near large bodies of available cooling
water desirable if not necessary.
The use of thermophi1ic bacteria as the active microorganism may be
another possible way to circumvent the cooling problem. Here, however,
new data must be developed on the usefulness of the product for foods
and feeds before markets would be available.
It appears that in any event the fermentation operation will be
responsible for a large portion of the total production cost of the
product yeast. Process improvements in the aeration, mixing, cooling,
separating and dewatering steps can result in useful economic gains.
115
-------
MARKET ANALYSIS FOR YEAST
YEAST IS A COLLECTIVE NAME for those fungi which possess a
vegatative body consisting, at least in part, of simple individual
single cells. Their use, for the purpose of this study, will be largely
as protein and vitamin supplements in human foods and animal feeds. To
better understand the applications and the needs of the protein field,
brief discussions of the technical aspects and problems of protein
acceptance will precede the market analysis.
A. The Protein Problem
In the words of Dr. Ricardo Bressani of the Institute of Nutrition
89
of Central America and Panama (INCAP) : "the idea of a hunger-free
world has stirred the imagination of men everywhere."
The scope of the problem has been outlined in many articles,
90 91 93 94 9? 96 83 92 97
reports^ '* and bul letinsy:>'yH'^«yo and discussed at conferences. >y'3/
The observations that today there are over 300 million children who,
for lack of sufficient protein and calories, suffer retarded physical
and mental growth and that the present population of three billion people
is expected to double by the year 2000 have been discussed and documented.
It is the problem of feeding this mass of humanity in an acceptable
and adequate manner that is the cause of great concern.
90
One U.N. report states : "It is now recognized that the protein
problem is reaching a critical stage. It is essential that the United
Nations family urgently take action aimed at closing the present gap
between world protein needs and protein supplies and at preventing even
more widespread protein deficiency in future generations. ... there
is no single or simple solution to the complex problems of providing the
required immense quantities of proteins ... in form acceptable to the
final consumer."
98
Wilcke states : "According to history, as the economic level of
a given population improves, the consumption of foods from animal
sources increases."
92
Abbott in his presentation on Protein Supplies and Prospects
observed that "while animal protein resources are rising in the
developed countries, in the developing countries the total per capita
16
-------
protein supply has declined by about 6% since World War II, with
increased dependence on protein from grain. On an average, present
supplies are generally adequate for nutrition; in practice, variations
in individual requirements and economic and social impediments to
distribution mean that substantial segments of the population do not
receive enough."
Data on the various aspects of population and protein supply
are shown in Tables XXXVII through XLII.
The general overall conclusions reached by investigators in this
field are:
1. A world protein shortage does exist.
2. Additional protein needs of 2.8 billion pounds per year
are predicted for the current rate of population growth.
3. Based on present methods of production, the world population-
protein gap will widen.
k. Although animal protein is a preferred diet for most people
the productivity and cost make this source less available to
segments of the world population which have the greatest need.
5. New and unusual sources of protein indigenous to the popula-
tion must be developed into nutritious and highly acceptable
foods.
6. The protein sources introduced should be utilized to their
maximum value as protein and not squandered as calories.
7. The food product developed must compete successfully in the
market place.
117
-------
TABLE XXXVII; PROTEIN SUPPLIES PER CAPITA BY MAJOR FOOD GROUPS AND REGIONS92'153
Vegetable Protein
Grains
Starchy
Roots
Pulses
Oil-
seeds ,
and
Nuts
Vege-
tables
and
Fruit
Meat
and
Poul-
try
Animal Protein
Eggs
Fish
Milk
and Milk
Products
Grams per Day
North America
Austral ia and
New Zealand
Western Europe
Eastern Europe
and USSR
Latin America
Far East
Near East
Africa
Europe, North
America,
Austral ia
New Zealand
Argentina
Paraguay
Uruguay
Far East, Near
East, Africa,
Latin America
(except
Argent ina,
Paraguay and
Uruguay)
World
15.7
24.3
30.5
48.3
26.5
32.2
48.5
32.2
33.4
33.2
33.4
2.3
2.4
4.4
8.2
2.7
1.8
0.7
7.1
5.2
2.3
3.2
4
2
5
2
10
12
9
9
3
11
9
.7
.1
.0
.0
.7
.0
.5
.0
.8
.6
.0
4
3
4
2
2
1
3
1
3
1
2
.6
.1
.1
.5
.8
.7
.6
.7
.6
.8
.4
31.9
36.8
16.2
12.9
13.8
3.0
4.6
5.8
19.8
3.8
8.8
6.0
3.5
3.1
2.2
1.2
0.4
0.5
0.4
3.3
0.4
1.2
2.5
2.2
2.4
1.9
1.5
2.2
1.1
1.3
2.4
1.9
2.3
25.3
19.5
17.3
16.1
7.4
2.2
7.4
3.5
18.5
2.9
7.7
Total
93
94
83
94
67
56
76
61
90
58
68
118
-------
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TABLE XXXtX: PROTEIN REQUIREMENTS AND SUPPLIES AVAILABLE92'153'15**
(Grams per capita daily)
U.S.A.
Canada
Austral ia
New Zealand
Britain
France
Germany, Federal Republic
Greece
1 reland
Italy
Sweden
Switzerland
Yugoslavia
Argentina
Brazil
Chile
Colombia
Mexico
Peru
Cey 1 on
China (Taiwan)
India
Japan
Pakistan
Phil ippines
Israel
Libya
Turkey
U.A.R.
Mauritius
South Africa
Requi rements
40
42
45
44
44
47
44
49
45
46
48
44
52
42
45
46
48
44
48
47
42
48
43
46
46
44
47
45
45
42
41
Supp] ies
92
95
92
105
86
96
79
95
96
77
81
90
96
98
61
77
48
68
58
45
57
51
67
46
47
83
53
90
76
46
73
121
-------
TABLE XL: DISTRIBUTION OF WORLD'S POPULATION AND FOOD SUPPLIES,
BY REGIONS (1957-1959)96'10**
Regions
Far East (incl
Near East
Africa
Latin America
Europe (incl.
North America
Oceania
. China, mainland)
USSR)
% of
Popula-
tion
52.9
4.4
7.1
6.9
21.6
6.6
0.5
% of
Total
27.8
4.2
4.3
6.4
34.2
21.8
1.3
Food Supp 1 i es
Animal Crops
18.5 44.2
2.8 5.5
2.8 6.3
6.7 6.5
38.4 26.2
29.2 10.4
1.6 0.9
World
100.0 100.0
100.0 100.0
TABLE XLI: AVERAGE YIELDS OF MAJOR CROPS AND CATTLE PRODUCTS BY
GROUPS OF REGIONS (1957-60)96']°^
Commod i ty
Crops, 100 kg/ha.
Wheat
Rice, Paddy
Other cereals
Starches
Pulses
Cattle products
100 kg/head of cattle
Less
Developed
Regions
19.
9.
74.
6.
Developed
Regions
2.6
13.3
38.4
18.0
122.2
6.5
13.9
World
11.9
19.2
13.3
97.1
6.2
6.5
Meat and milk in terms of milk equivalent, taking 1 unit of meat as
equal to 10 units of milk. Averages for 1958-60
122
-------
TABLE XLII: CURRENT CONSUMPTION LEVELS FOR INDIA, GROUP I COUNTRIES
GROUP II COUNTRIES. AND THE WORLD ASAWHOLE *155
Cereals
Starchy roots
Sugar
Pulses and nuts
Fruits and vegetables
Meat
Fish
Eggs
Milks and milk products
(excl. butter)
Fats and oi Is
Calories
Animal protein, g.
Total protein, g.
Fats.g.
Calcium, mg.
Iron, mg.
Vitamin A,IU
Thiamin, mg.
Riboflavin, mg.
Niacin, mg.
Ascorbic acid, mg.
India
Grams
375
30
45
65
80
4
7
1
140
11
1,970
6
51
27
446
15
1,432
1.3
0.6
7
26
Group 1 ,
excl .
India
per Person
393
229
26
50
191
37
28
5
64
12
2,190
10
60
36
293
»3
2,945
1.6
0.7
14
83
Group
la
per Day at
389
189
29
53
169
30
24
4
79
12
2,150
9
58
34
324
14
2,642
1.5
0.7
14
72
Group
Mb
Retail
328
316
88
16
362
152
34
33
573
47
3,060
44
90
106
1,099
17
5,555
2
2
19
116
World
Level
370
227
47
42
227
67
27
12
228
22
2,420
20
68
56
557
15
3,516
2
1
15
85
Far East, Near East, Africa, and Latin America, excluding River Plate
countries.
Europe, North America, Oceania, and River Plate countries.
Protein requirements and the value of various sources of protein
, . . i_. , , . JU 89,92,99,100,101,102,103,104,105,106
have been investigated and reviewed by many. »""> > > » * > "»
In October 1963, the Joint Food and Agriculture Organization-World Health
Organization (FAO/WHO) recomm nded the following basis for assessing protein
requ i rements;
123
-------
Age Group Protein Requirements
(GRAMS/Kg of BODY WEIGHT)
1-3 0.9
'4-9 0.8
10 - 15 0.7
16 and over 0.6
Other factors such as the value of the type of food protein in
terms of net protein utilization or protein efficiency ratio, sex,
pregnancy, etc. enter into the overall requirements.
The value of a food protein is closely associated with the amino
acid balance of the food and the human system's ability to assimilate
these useful materials. Tables XLIII through XLVI show amino acid
compositions and vitamin contents for various protein sources.
Studies on protein utilization have been conducted. Work in this
89
area is documented in the bibliography of papers by Bressani, and by
Morrison and Rao.
Competing sources are being proposed and developed to alleviate the
shortage in world protein. Although future competition in process and
product development will increase, present predictions are that there
will be room for everyone that has the ability to meet the requirements
of the market place. The major areas of protein development both usual
and unusual are outlined below.
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TABLE XLIV; ESSENTIAL AMINO ACID CONTENT OF YEAST AND OTHER PROTEINS (ma/aN)
89
Amino Acid Torula Brewer's Casein Cottonseed Soybean Egg
Tryptophan 86
Threonine 315
Isoleucine 449
Leucine 501
Lysine 493
Total Sulfur
amino acids 153
Phenylalanine 319
Valine 392
Arginine 451
Histidine 169
TABLE XLV:
96
318
324
436
446
187
257
368
304
169
ESSENTIAL AMINO ACI
Amount
Essential Amino
Acid LSU ESSO
Arginine
Hi st idine
1 sol eucine
Leucine
Lys ine
Methionine
Phenylalan
Threonine
Val ine
Tyros ine
Half Cysti
Tryptophan
Not
9.84
2.38
4.57
10.82
6.69
1.63
ine 4.10
5.52
10.60
2.57
ne 2.86?
*
reported
*
*
3.6
5.6
6.5
2.0
2.9
4.0
4.5
*
0.6
*
84 74
269 221
412 236
632 369
504 268
218 188
339 327
465 308
256 702
190 166
D CONTENT OF THE S
INGLE CELL
86 103
246 311
336 415
482 550
395 400
195 342
309 361
328 464
452 410
1 49 1 50
PROTEINS
(g/100 g protein)
Ideal Amino
British Torula Acid Pattern Soybean
Betroleum Yeast bv FAO Protein
*
*
5.3
8.1
7.6
1.7
5.7
5.8
5.7
*
1.0
*
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2.2
6.4
8.0
8.5
1.5
5.1
5.1
5.6
4.3
1.0
1.37
*
*
4.2
4.8
4.2
2.2
2.8
2.8
4.2
2.8
2.0
7.0
2.5
5.8
7.6
6.6
1.1
4.8
3.9
5.2
3.2
1.2
1.37
126
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Grains89'92'102'105'108:
Grains provide nearly half of man's total protein supply, and the
bulk of his calorie intake. Although grains have been a staple in the
human diet for centuries their amino acid balance (See Table XL!I I) is
below the standards of nutrition set forth by FAO. Their wide supply
and general acceptance as foods has spurred research efforts to increase
yields of the traditional grain crops. Dr. Edwin Mertz and co-workers
at Purdue University have succeeded in producing a maize with improved
protein quality. This work is truly revolutionary and should stimulate
research of this type on other grain crops.
A tremendous effort has been expended in producing new and
acceptable foods with balanced nutritional values from grains and high
protein supplements such as Torula yeast. Recent efforts to fortify
cereals directly with amino acid values such as lysine and tryptophan
show excellent technical and economic promise.
Oilseeds and Pulses92'101'103'10*:
The rapidly growing world protein need has directed major attention
to the food use of oilseed proteins. They play a vital role in reliev-
ing protein malnutrition in many areas where animal products are too
expensive. Oilseed cakes constitute the main untapped sources of
protein for human consumption in India, for example. This protein
source is currently employed as an animal feed or fertilizer due to its
condition after primary processing for oil removal. Refined oil recovery
processes and toxin removal methods have been developed as have appealing
and nutritious foods from these protein sources. Their application
increases the prospects for expanding production of the wide variety of
species available in this group.
109
B.F. Buchanan noted that "there is potentially as much protein
available from today's oilseed production as from all edible animal
products." This would be enough, at minimum values, to suoply the protein
requirement of an additional one billion souls.
«. 89,110,111
Yeasts :
Yeast consumption by man as a component of unfined alcoholic
beverages, cheeses and yoghurt has been going on through all of recorded
128
-------
history, and most probably before. The amount consumed may have supplied
a useful portion of early man's protein requirements as well as his needs
for the valuable B vitamins. Current uses of yeast other than in fermenta-
tion and baking applications include their incorporation in cereal foods
as a source of vitamins and amino acids, canned baby foods, canned soups,
sausages, sandwich spreads and other products where "meat" flavors are
required. It has been stated that food yeasts offer the greatest potential
for development of all current sources of protein concentrates. This is
due to the high efficiency of yeast in the utilization of carbohydrate to
synthesize protein. If available by-product yeast from the top 22
breweries were added to the yeast that would be produced if all molasses,
sulfite waste liquors and whey were converted to yeast, an annual produc-
tion of one million eight hundred and fifty thousand dry tons would be
realized in the United States. The utilization of this material is
discussed in the marketing section below.
92 98
Animal Protein ' :
Livestock protein foods, including milk and eggs, are preferred by
most consumers. Consumption rises sharply with income. The conversion
of grain protein to animal protein is rather inefficient however, see Figure 18,
and in countries where total protein supply is limited, direct consump-
tion of grains by the populace is practiced to a higher degree. The
expansion of an animal protein economy within a given country will depend
on the nations economic growth factor and improvements in the technology
of animal husbandry. The ability for a nation to support livestock is
presently affected by the amount of arable land available for growing
feed.
Fish92'100:
The consumption of fish is limited by marketing problems in many
parts of the world. However, fresh,dried and fermented fish find their
way into the diets of many peoples. Approximately twenty-five percent
of the forty-five million tons of fish caught today is converted to fish
meal and incorporated into animal feeds. The prospects for fish protein
are of great interest since thejr production does not require the
expenditure of resources that are directly useable as food and the supply
is estimated at two and one half times the present consumption. Then too,
129
-------
Conversion of Total Feed to Edible Carcass
Beef
Swine
Broiler
Hen
D
10 20 3.0
Percent Efficiency
Conversion of Protein Ingested to Edible Protein
Beef
Swine
Broiler
Hen
1Q 20
Percent Efficiency
30
FIGURE 18: CONVERSION OF INGESTED FEED TO FOOD
98
(30
-------
the new technologies for producing fish protein concentrates (FPC) from
"rough fish" extend the supply of fish protein available for human
consumption. Technological and economic problems still exist, but the
outlook for FPC is very promising.
.. 112,113,11^,118- .106,115 . D . 116,117
Algae, ' ' ' Fungi ' and Bacteria ' :
Work has progressed in producing algal, fungal and bacterial
protein values in a useful manner. The technologies have progressed
to demonstration plant sizes for growing algae on sewage wastes and
producing bacterial protein on hydrocarbon substrates. Fungi can
convert carbohydrate materials such as potatoes, corn, sugar cane,
bagasse, etc. to protein in an effective manner (see Table XLVIl).
Product separation and growing techniques are reported to be very good
for selected species.
Discovery of a blue-green algae, Spirulina, that has been in use
as a food in central Africa since ancient times, has increased the
interest in this class of protinaceous material. Amino acid composi-
tions of Spirulina compared with the FAO standard are shown in
Table XLVIlI. Algae production is ideally suited to the sunny hot
climates where photosynthesis activity is at the highest levels.
The present anticipated use of these "new" protein foods is as
high protein supplements in animal and poultry feeds. Eventual use as
components in foods for human consumption is a logical further step.
The useful concept employed by these unusual protein sources is their
production from waste products or materials of non agricultural origin
that are in great supply.
131
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TABLE XLVIII: ESSENTIAL AMINO ACIDS113
(g/lOQq of proteins)
1 sol eucine
Leucine
Lys ine
Phenylalanine
Tyrosine
Total sulfur amino acids
Methionine . .. .. ..
Threonine
Tryptophan . . . . . . .
Va 1 i ne . .. .. .. ..
I.F.P.
Spi rul ina
6.03
8.02
4.59
4.97
3.95
1.80
1.37
4.56
1.40
6.49
Standard
Combinat ion
F.A.O.
4.2
4.8
4.2
2.8
2.8
4.2
2.2
2.8
1.4
4.2
B. Current Market Situation for Yeast
Yeasts represent one of the richest sources of vitamins, particularly
the B complex group, and amino acids available today. Yeast protein is
a good source of lysine and has sufficient quantities of other essential
amino acids such as tryptophan and threonine. Yeast is however deficient
in methionine which can be corrected by supplementation with grains or
oilseeds that have an abundance of this material.
89
Results of various feeding studies, summarized by Bressani, show
the yeasts as a group to be generally acceptable as a protein source or
high protein supplement for both human and animal consumption. Where
the basic diets are deficient in methionine this component must be
added for maximum growth to accrue. In poultry feeding studies torula
yeast was used satisfactorily as the sole protein supplement and in
some cases yeast was the sole protein source.
Yeast, then, has been traditionally used as a vitamin and protein
supplement in feeds and represents an accepted component for good
nutrition.
133
-------
Raw Materials Economics '
A real appraisal of the economic position of the different available
raw materials for fermentation to yeast must consider the fermentation
industries as a group. Most of the appraisals attempted in the past are
119 120 121 122
incomplete in this sense and generally out of date. » » > ^
general comparison of the possible competitive positions of the major
raw material groups is considered in the following paragraphs.
The major source of carbohydrate for the fermentation industries
is molasses. It is a waste material of the cane and beet sugar industry
and as such represents a potential liability if suitable utilization
1 23
outlets such as the fermentation industries did not exist. Gabriel
has indicated that cane sugar manufacturers could better afford to
give away their molasses than to go to the expense of disposing of it.
Certainly, if this is the case, molasses will always maintain a
competitive position in the market and represents a sugar cost that
competing processes must approach, other values being equal. An increas-
ing tendency to utilize molasses in countries where it is produced may
eventually limit its availability for export.
The utilization of waste liquor from sulfite pulp mills as a
fermentation substrate has been pursued in the United States, Canada
and to a larger degree in the Scandinavian countries. Yeast and ethanol
production facilities have been established using this raw material.
The Candida utilis yeasts, commonly called Torula, produced on this
substrate have the ability to utilize both the hexose and pentose
sugars available. The development of the market for this "new" type
yeast has lagged in the U.S. in spite of its favorable sales price
position. There has been a general hesitancy on the part of the
sulfite paper mills to enter the fermentation business even though this
utilization of wastes represents an attractive disposal system.
Relatively large capital costs and a new marketing area have limited
the participation by the sulfite pulp mills in this field.
Another waste product that has achieved commercial size as a
125
substrate for fermentation operations is whey, or lactose from whey.
124
Smith and Claborn have estimated that 2.7 billion pounds of lactose
could be obtained from dairy by products and to a large extent made
-------
available for fermentation.
The economic position of wood waste, agricultural residues and
other cellulosic materials have been and no doubt will continue to be
employed in countries that cannot raise enough food crops to meet the
requirements of their populations. A case in point is wartime Germany
where saccharification of wood wastes with subsequent fermentation to
yeast was developed and practiced to supplement the protein needs of
the nation. Current efforts in Russia and Eastern Europe to grossly
increase their productive capacity of food and feed yeasts will at
least in part consist of cellulose conversion mechanisms. The utiliza-
tion of cellulosic materials as a raw material for the production of
fermentation substrates in the United States will require special
circumstances. Favorable conditions of location, waste availability
and costly waste disposal situations are some factors that will provide
the driving force necessary for the construction of facilities to convert
cellulose materials to fermentable sugars. New process developments in
the fields of hydrolysis and enzymatic conversion techniques will add
to the desirability of this raw material source.
Current Yeast Production:
Peppier states : "In the United States today yeast is produced
as a major end product by eight manufacturers operating at sixteen
locations. Fourteen of these factories (six companies) will produce in
1967 an estimated 58,500 tons of yeast dry matter in the form of bakers
yeast, or about 65% of the total domestic harvest £see Table XLIXT The
remaining third of annual production comprises two small amounts of
primary food and feed yeast grown on spent sulfite liquor and whey,
and a major portion of secondary yeast recovered as brewers yeast."
135
-------
TABLE XLIX: U.S. YEAST PRODUCTION
(Estimated 196?)
Ill
Compressed bakers yeast
Active dry yeast
Food grade dried yeast
Saccharomyces sp.
Candida uti 1 is
Feed yeast
Saccharotnvces SP.
Candida ut;i 1 i§
Extracts, autolysates, etc.
Total
Dry Tons
56,000
2,500
15,000
1,000
10,100
1 ,800
3,700
90,100
Substrates
Molasses
Molasses
Grain, molasses,
Sulfite liquor
Grain, molasses,
Sulfite 1 iquor
Grain, molasses
whey
whey
Surveys of yeast manufacture in 1963 and 1964 for the domestic and
world markets is summarized in Tables L and LI. European output of
dried yeast represents two thirds of world production. This large
quantity is used mainly for animal feed purposes and is reportedly
grown on waste materials, wood hydrolysates and beet molasses.
A breakdown of raw material availability for fermentation (alcohol)
and yeast end-products by carbohydrate source is shown in Table Lll.
U.S. Market Outlook :
American Food and Feed Yeast Enters the Market as: :
1. A rich supplementary source of vitamins, growth factors,
amino acids, and mineral elements for animal, fish, and
poultry feeds, and for substrates in other fermentation
processes.
2. A source of vitamins and nutritional factors used in
fortifying human food products.
3. A source of vitamins for Pharmaceuticals.
k. A source of amino acids, protein fractions, and extracts
for food and pharmaceutical use.
5. A source of enzyme materials.
6. A raw material for various other fractionating processes
in the pharmaceutical, chemical, and food industries.
136
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TABLE L: UNITED STATES YEAST OUTPUT, 1963'11>126
(Dry Tons)
Bakers Yeast
Other Yeast Products:
For food purpose
For feed use
Total
^3,800
8,838
16,281
68,999
TABLE LI: WORLD YEAST PRODUCTION111'127
(Dry Tons)
Europe
North America
The Orient
South America
Africa
World Total
Bakers Yeast
67,600
61,000
12,900
6,300
2,350
150,150
Dried Yeast
125,500
37,500
21,300
1,200
2,200
187,700
TABLE LI I: CARBOHYDRATE MATERIALS USED FOR YEAST FERMENTATIONS111'128'129
(Un ? ted States 1965)
Molasses
Sulfite Liquor
Whey
Fruit Products
Grains
Unit
mi 1 1 ion gal .
mill ion gal .
mi 1 1 ion gal .
1000 tons
1000 tons
Supply
613
12,000
3,530
k,62k
15^,700
Utilizat
Fermentation
67(11%)
298(2.5%)
10(0.3%)
2,45M53%)
3,569(2.3%)
ion
Yeast
50(8.2%)
75(0.6%)
5(O.U%)
Nil
137
-------
Food Yeasts:
The largest segment of the domestic yeast industry, molasses grown
yeast, is expected to maintain its present annual growth rate of 2 per
cent which is consistent with population growth. Some increases
might accrue from heavier usage of leavening yeast in modern continuous
dough making systems in the baking industry.
New large scale uses of yeast for human consumption in the United
States are not apparent at this time. American yeast production might
find increased outlets in the export field where new high protein foods
such as Incaparina,contain ing 3 per cent torula yeast ,are being used in
increasing volume (see Table LI I I). Local production of yeast for this
purpose and direct supplementation of the foods by the required amI no
acid components will be strong competitors for this market.
TABLE LIN: PRODUCTION OF INCAPARINA IN LATIN AMERICA103
(Pounds)
Year
1961
1962
1963
1964
1965
aNot
First
--
68,772
63,134
475,055
720,458
produced
Trimester
Second Third
44,250
9,568
154,464
237,411
832,648
because of low
100,755
128,515
106,977
722,844
ava i labi 1 ity
Fourth
100,731
a
163,995
728,034
of cottonseed
Total
245,736
206,805
488,570
2163,344
flour.
Animal Feeds:
The value of high protein feed is illustrated by W.E. Huge in his
article in Soybean Horizons Unlimited. Comparing output/feed condi-
tions over a thirty year span, Mr. Huge recorded the following data:
138
-------
1930 1959
pounds feed/pound poultry 5 2.5
pounds feed/pound tyrkey 6.5 3.6
pounds feed/dozen eggs 7.3 4.0
eggs/hen/ycar 123 195
Recent data lowers the feed-poultry figure to less than two
pounds of feed per pound of poultry.
The increase in livestock feed concentrate use is projected to rise faster
than livestock production which will be favored to grow faster than
population due to increased per capita consumption. High protein
feedstuffs is estimated to increase faster than that of other
concentrates. Figure 19 shows average feed grain and feed
concentrates fed during 1948-1950 and 1958-1960 with predicted
consumption for 1980. The 1958-1960 figures when compared with 1980
figures show an annual consumption increase in feed concentrates of
86 million tons with an annual growth rate in consumption of about
2.3 perccent . Since high protein feedstuffs utilization is predicted
to increase at a greater rate than concentrates in general the 2.3
per cent per year increase should represent a conservative figure
for high protein feed needs. Figure 20 summarizes this requirement
132
based on current high protein feed availability of 18 million tons.
The separate curve showing soybean meal and animal meal components
are based on current values and the 2.3 per cent progression. Yeast
substitution levels as shown are based on 100 per cent substitution
for soybean meal, values adjusted for protein content, and 50 per cent
substitution for animal protein values. Soybean meal was calculated
at 44 per cent protein, animal meal at 50 per cent and yeast at
50 per cent. The choice of 100 per cent substitution for soybean
meal and 50 per cent replacement of aminal meal by yeast is based
89 122
on animal feeding studies reported in the literature. '
Price fluctuations, converted to price per pound of protein,
for soybean meal, animal and fish meal are shown in Figure 21.
Data on feed price and consumption is available from the U.S.
Department of Agriculture's Economic Research Service. ' ' '
139
-------
Total Concentrates
ZZ!
250
200-
150-
100-
50-
Feed Grains
19^8-1950
Average
1958-1960
Average
1980
Projected
FIGURE 19: TOTAL CONCENTRATES AND FEED GRAINS FED
131
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Any new feed components will have to compete favorably with the
present market to be considered as a feed protein source. A case in
point is the evolution and growth of urea feeding to ruminants. The
utilization of non protein nitrogen by ruminants allows the formulation
of corn-urea, sorghum grain-area mixtures that represent a significant
price advantage for these feeds. Recent prices show $25 to $30 per ton
price reductions for the urea based feeds over soybean or cottonseed
132
meal feeds. Competition for the poultry, turkey and hog feeding
market which cannot utilize urea feeds will probably result in increased
downward pressure on the price of the traditional high protein sources.
Oilseed protein is a by product of the vegetable fat and oil market and
is thereby largely controlled by the demands for these commodities.
Requirements for vitamin supplements to feeds represents a smaller
but significant market. 6 vitamins and D vitamin supplements can be
obtained from dried yeast and irradiated yeast respectively. The total
market for this application is perhaps ten per cent of the high protein
122
feed market. Competition from other yeast sources such as brewer's
yeast is to be expected. The magnitude of the market is price oriented
with the ten percent figure cited above as being the maximum value pre-
dictated on maximum beneficial additions of vitamin supplements to
livestock rations. The relatively high current cost of yeast makes it
desirable to attempt to satisfy the animal's vitamin requirements through
careful selection of feedstuffs which make up the ration and to use yeast
only when the nutrient requirements cannot be satisfied by other feeds.
The livestock feed market is perhaps the best potential domestic
application for the large volumes of yeast that can be produced on the
cellulose wastes available. Entries in this field to date have been
limited to special situations such as the use of torula yeast additives
7 1
86
with dried citrus wastes for feeds in Florida. ' The principal current U.S. outlet
for torula yeast is as a poultry feed supplement.
-------
Price Considerations:
Current prices and ranges based on quantity discounts and location are
recorded in Table LIV for various protein sources. Current sales prices
for Torula yeasts produced on sulfite waste liquor at 27-29 cents per
pound of protein equivalent is considerably above that of competing
protein sources such as soybean meal at 8-14.8 cents, animal meal at 8-12
cents and fish meal at 11 to 14 cents per pound of protein for the livestock
feed market.
For yeast to compete significantly in the feed market an operating cost
in the range of 10 to 12 cents per pound of protein product appears
desirable.
TABLE LIV: ALTERNATE PROTEIN SUPPLY SOURCES
Material
in n4
Soy Meal and Flour " ' 5
1 38
Soy Protein Cone.
1 ^R
Soy Protein Isolate
Fish Meal (feed grade)13
1 18
Fish Protein Cone.
1 38
Cottonseed Flour
Wheat (Kansas City) 138
Wheat Flour
Dry Skim Milk'38
Animal Meal (feed grade)
Chicken (dressed)138
Beef (retail)138
Yeast - Torula (Sulfite waste) ] ' ' 139'
140,141
S. Fragilis (Whey waste)
Brewers Yeast
Brewers Yeast Debittered
Bakers Yeast
Price/Pound
(cents)
3.5-6.5
21.5
_
6.3-8.5
10-16
11
220/bu.
6.6
14.4-21.0
4.1-6.3
30
80
15-16
19-25
12-15
23-38
21-42
Price/Pound Protein
(cents)
8-14.8
26.5-35
36.3-39.3
10.5-14.2
13-20
20
30
60
40-60
8.2-12.6
150
444
27-29
35-46
26.6-33.3
46-76
42-84
144
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Product Volume Considerations:
At a refuse production rate of k.S pounds per capita per day consisting
of *f6.6 percent cellulosic base organic matter a city of 200,000 population
would have an input to a hydrolysis plant on a 100 percent recovery basis
of (k.S x 0.^66 x 200,000)72000 = 210 tons/day
Fermentable sugars from this plant would be 82 tons per day based on
a three stage hydrolysis plant resulting in a yeast production of ^1 tons
per day and an equivalent protein production of 20.5 tons per day. Yearly
production rates based on a 300 operating day year would be 6,150 tons of
yeast protein for a city of 200,000 population. Considering the current
U.S. population at 200 million people a maximum, albeit unrealistic, production
of 6,150,000 tons of yeast protein per year can be realized from municipal
refuse sources in the United States alone. To convert back, this represents
12.3 million tons of yeast.
Since the type yeast produced on waste will be the torula strain due
to the need for converting pentose as well as hexose sugars, it will not be
applicable to the major food uses in the U.S. where the Saccharomyces
cerevisiae is normally employed. The export food market for such final
products as Incaparina may utilize some of the volume available. Present
needs for the I neap program are a requirement of approximately forty-five
tons of Torula yeast per year based on a 3 percent addition to the last
four quarters production noted in Table LIM. This yearly yeast requirement
could be met by converting the refuse from one city of 200,000 people in
little more than one day.
It is apparent that the livestock feed market is the only current
volume outlet for the large tonnages of product available from this process.
Annual maximum consumption of yeast protein supplements in animal feeds is
estimated in excess of 12 million tons at present livestock production rates,
Figure 20.
C. Economics of Yeast from Wastes
Data has been developed in earlier sections of this report on the
various costs of raw materials, plant and operating costs for hydrolysis,
and the plant and operating costs for fermentation of the sugars produced.
-------
The data as summarized here is based on multiple choices of the raw
material source and a 500 ton per day feed rate to the hydrolysis plant.
The size community needed to support this facility on the basis of raw
material requirements is about one half million people for urban organic
refuse, a city the size of Philadelphia for 20 percent additional recovery
of paper wastes, or the combined output of two high efficiency cane mills
J34
for a bagasse feed. Current molasses costs are included as a comparison
factor for hydrolyzate sugars.
TABLE LV: COST SUMMARY ON SUGAR FROM ORGANIC WASTE HYDROLYSIS
(Basis: Cost of raw sugar)
Sugar Source
Molasses (1966-196? range)13**
Bagasse
Wastepaper, No.l mixed
Mixed Urban Refuse
Organic Urban Refuse
Cost/pound
(cents)
1.2-1.6
0.25-0.75
0.20-0.60
0.125-0.225*
0.125-0.225*
-I-*'-
Cost/pound of sugar
(cents)
2.4-3.2
3.03-^.32
2.91-3.93
2.08-2.34
1.81-2.07
J.
Credits based on municipal dumping fees.
**
Costs other than molasses based on a 500 ton per day 3 stage, continuous
hydrolysis plant. Table XXVII.
The production costs for sugar from organic waste materials appears
reasonably competitive with the main market source of fermentable sugar,
molasses. The most recent molasses prices are the high end of the range
noted above. However, molasses is expected to compete favorably with any of
the prices developed for alternate market sources for sugar due to the fact
that it is a liability waste commodity for the sugar industry. Alternate uses
and disposal costs are the key elements in the molasses market.
The low bagasse sugar costs should be considered as significant when
evaluating this material, as the additional costs represented by the higher
range are for loading and shipping purposes. It would appear that the
hydrolysis operation at a sugar central is the only desirable route to take
146
-------
when considering bagasse as the raw material. The supply of bagasse is such
that no upward price fluctuations are envisioned.
Wastepaper as a raw waste source appears, from the numbers presented,
to be more competitive than is actually the case. It would be unrealistic
to assume that any steady supply of wastepaper would be available at the
low end of the range indicated. Although the prices cited represent a
ten year price range for this commodity, the entry of a big consumer into
the market, such as a wastepaper hydrolysis plant, would tend to keep the
prices at the high end of this range, and perhaps, depending on demand,
exceed these figures entirely. Since the raw material represents approximately
41 percent of the product cost for a 500 ton per day plant the effect of the
market cannot be minimized. As noted in Table VII, of this report prices for
No. 1 mixed paper ranged to 35 dollars per ton in 1951 this would result
in a hydrolyzate sugar cost of 6.88 cents per pound. It would appear that
the market risks for wastepaper as a sole raw material source are too
great for serious consideration.
The utilization of urban refuse is in general the most attractive
waste commodity evaluated in this study. The cost factors or credits,
however, are subject to much local influence. The choice of hydrolysis-
fermentation as contrasted to sanitary landfill or incineration as a
refuse disposal means must be evaluated on a local basis. The existence of
local markets for secondary materials such as metals and paper, or for
garbage for hog feeding will influence decisions. But again, these are
specific decisions for individual municipalities. On a general basis, the
cost range of 1.81 to 2.3^ cents per pound of hydrolyzate sugar appears to
be competitive with its market alternate for yeast production, molasses.
These costs have been developed on the best information available today
and include factors of municipal dumping fees, segregated refuse and sorting
operations for non-segregated refuse.
The conversion of the hydrolyzate sugar to yeast and its economic
position as a potential animal feed source is summarized below. Costs of
significant livestock feed protein is included for ease of comparison as is
the sales price of Torula yeast from sulfite waste liquor.
-------
TABLE LVI; SUMMARY-YEAST COSTS VS ALTERNATE ANIMAL FEEDS
Protein Source
134
Soy bean meal
. . , ,134,138
Animal meal
Fish mea!13/f
Torula yeast (Candida utilis)
Sulf ite Waste Liquor'11
Bagasse
Wastepaper
Mixed Urban Refuse
Organic Urban Refuse
Percent Protein
44
50
60
55
Cost/pound
(cents)
3.5-6.5
4.1-6.3
6.3-8.5
15-16
10-14. 3
9.8-13.6
8. 1-10. U
7.6-9.8
Cost/pound protein
8.0-14.8
8.2-12.6
10.5-14.2
27-29
18.2-26
17.8-24.7
14.7-18.9
13.8-17.8
The protein cost figures from the various sources of hydrolyzate sugars
are based on the sugar price ranges summarized in Table LV, a 50 percent
utilization factor in the conversion to yeast and the maximum and minimum
fermentation costs developed in the two cases in the Fermentation Process section
of this report. The cost ranges then represent the total spread of values for
the conditions considered.
It can be seen from Table LVI that the low range of the hydrolysis-fermentation
system protein cost is comparable to the high range of the traditional animal
feed protein price used in the U.S. today. Since conservative estimates were
used in developing the hydrolysis-fermentation costs, it may be presumed that
these numbers may be improved upon in actual practice.
It must be recognized that this cost situation results from a set of
unique circumstances. They are: 1) The availability of segregated urban wastes,
2) the willingness of the municipality to pay a "dumping fee" to the hydrolysis
plant for waste disposal and 3) the availability of a large body of cooling water
for the fermentation plant. Alternates such as mixed urban refuse with a
satisfactory secondary material market may be substituted as can other local
situations which influence the cost picture.
The availability of a local feed market will enter into the total evaluation
as it did in Florida where Torula yeast was locally produced and mixed with
citrus wastes as a feedstuff.
At the above calculated prices it is expected that yeast can capture a more
148
-------
significant segment of the animal feed market than it currently enjoys.
However, significant improvements in cost must be achieved before yeast can
become a major factor in the animal feed field.
Cost levels developed above should result in a better market penetration
in the human food and vitamin supplement field of animal feeds. Although this
market is significantly smaller, and more complex, it presents an alternative
initial marketing route for these lower cost yeast products.
It must be remembered that the above comparisons have been made on a double
standard. That is, manufacturing costs for the hydrolysis-fermentation
yeasts compared with market price for the other protein sources. The application
of proper levels of return on investment and sales costs must be included in
the final analysis. They are not included here because of the wide variety of
circumstances that can be applied to alter the acceptable returns to industries
or municipalities. Then too, the total economic picture cannot be presented
without a definition of the valuable by-products that can be obtained from
the proposed processes. This detailed economic evaluation must, of necessity,
be based on laboratory studies of the processes involved.
D. A Brief Look into the Future
The concept that current situations will remain constant at elevated
levels of production activity due to population growth presupposes unlimited
land resources for producing the foods using todays technology. European
nations are currently producing more than three times North America's output
of dried yeast (Table LI) most of which is going to produce animal feeds.
Russia is planning to increase its yeast production to 900,000 tons per year
74 74 80
by 1970 and significant developments in Czechoslovakia and France
growing protein on petroleum substrates for the purpose of increasing livestock
feeds and to a lesser degree as food for direct human consumption are reported.
This appears to be a direct consequence of the inability of these nations at
their current level of population density to produce enough traditional crops
for animal feeding in a more economic manner.
If we assume that man will continue to value animal protein as a
prestigious diet and further concede that the current experience in Europe
must eventually become universal, we are obligated to devise systems that
149
-------
will produce animal protein and animal feeds that do not rely on traditional
farming concepts. If we add to these concessions the premise that efficient
utilization and disposal of wastes must be devised and put into effect, total
system designs such as the "City Farm Concept" discussed in the Appendix
must evolve.
Alternate concepts of "food factories" based on the development and
acceptance of non-agricultural manufactured foods and food concentrates are
already being seriously proposed in Eastern Europe.
150
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Product Engineering, 38(21): 37-44, Oct. 9, 196?
2. Spilhaus, Athelstan, et.al. Waste Management and Control Publicat ion 1400.
National Academy of Sciences - National Research Council, 1966.
3. U.S. Dept. of Health Education, and Welfare - Public Health Service,
Persona 1 Commun icat ion, Sept., 1967.
4. Rogus, Casimir A. Refuse Quantities and Characteristics. Proceedings
National Conference On Solid Waste Research, American Public Works
Assoc. Special Report No. 29, p 17-27, Feb. 1964.
5. Alarie, Albert. Can Garbage Become A "National Asset"? Compost Science
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6. Straub, H. Sammlung. Aufbereintung Und Verwertung Von Siedlungsab-Fallen.
Arbeitsgemeinschaft Fur Kommunale Abfallwirtschaft, Baden-Baden, I960.
7. Bell, John M. Character isitics Of Municipal Refuse. Proceed ings National
Conference On Solid Waste Research, American Public Works Assoc.,
Special Report No. 29, pp28-38, Feb. 1964.
8. Mun icipal Refuse Disposal, American Public Works Assoc., 1961
9. Harding, C.I. Recycling And Utilization. The Surgeon General's
Conference On Solid Waste Management For The Metropolitan Washington
Area, July 19-20, 1967.
10. Kaiser, Elmer. The Surgeon General's Conference On Solid Waste Management
For The Metropolitan Washington Area, July 19-20, 1967.
11. McKee, J.E. Dimensions Of The Solid Waste Problem. Proceedings
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162
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APPENDIX
The City Farm Concept
THE "CITY FARM CONCEPT" proposes the establishment of urban growing centers
for animal protein, utilizing to the fullest extent possible animal feeds
generated from urban refuse sources at their central collection point and
recycling solid wastes and liquid streams from the growing area for their
unused and available food and chemical values within the various operations
of the integrated plant. Animal protein products, meat, milk and eggs, will
be returned locally to the community and residual wastes from the total complex
will be treated by a central waste treatment plant resulting in a gross
reduction and controlled release of pollutants to the surrounding
environment.
Basis for the Concept:
2k
Walter Mercer stated : "Farms of th«» future will t«nd toward large,
wel1-managed, and mechanized business paralleling the trends already evident
in other industries. Surrounding the land, designated by law for agricultural
use, will be highly urbanized areas beginning abruptly where the farm land
ends."
1^3
Dr. P.H. McGauhey observed J\ "The rapid spread-out of cities,
popularly known as "urban sprawl", which followed World War 11 is widely
recognized as having revolutionized our concepts of urban life. ...
It has become evident in recent years that solid wastes management has
taken on a community-wide dimension involving all sectors urban, suburban,
and rural of the modern community."
]kk
John Wiley adds : "Our urban and suburban population growth has not
only resulted in greater use and increased values of land but has greatly
increased the quantities of solid wastes to be disposed of. While more
people require greater food and industrial production, they also crowd out
the farmer and agricultural industry either by demanding lands for their own
needs or by less direct means, such as annexing, zoning, or claiming nuisance
or health hazards."
23
Dr. E. Paul Taiganides concludes : "The trend in livestock production
is to automation. This is particularly exemplified by the recent history of
163
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confinement rearing of poultry and swine. During the last few years, many
of the problems associated with livestock and poultry production within a
confined area have been satisfactorily solved. Consequently, many farmers
are changing from pasture to pen confinement. In this manner, the full
advantages of central feeding, push-button operation and small land area
use per animal can be better utilized.
The trend to confinement production is firmly established. In the
poultry industry, units housing over one hundred thousand birds have been
in operation for quite some time now. Those who are close to the swine
industry indicate that, in the near future, by far the majority of hogs
will be raised in confinement units, each capable of marketing from 3,000
to 10,000 hogs per year. For example, in Red Oak, Iowa, pilot units de-
signed to market 10,000 hogs per year are now marketing 15,000 and a 10-
year expansion to 100,000 hogs per year is anticipated. The number of
dairy and beef cattle per farm is increasing with correspondingly less
area per animal."
Utilization and Disposal-
One method of utilizing urban organic refuse is the subject of this
report and will be used as the example process here.
Disposal of waterborne wastes and the amelioration of the carrier
waters is a steadily advancing science. Municipal systems discharging
high quality effluents suitable for reuse are a technological reality.
The application of these treatment systems to animal manures and in plant
reuse is feasible.
The nature of wastes resulting from livestock production has been
23
summarized by Taiganides. Waste loads from chicken ,swine and cattle
manure alone are equivalent to 10 times that of the human population in
the United States. Dead animals and birds,(mortality fate in hen produc-
tion is 1 percent per month) plus eviscera, feathers, blood etc. from meat
processing operations add to the overall wastes load to be considered. The
designer of systems handling these wastes must consider the odor nuisance,
fly breeding problems and the multitude of health hazards associated with
the wastes being treated.
-------
The physical and chemical properties of animal wastes are affected by
the particular characteristics of the animal, the feed ration and the environ-
ment. The quality of the feed influences the quantity of manure produced,
conversion efficiency of feed to animal protein and the chemical composition
23
of the manure. Taiganides states ' : "that most of the feed ingredients
of the animals will be excreted in the feces and urine. The amount of each
feed constituent found in manure depends on the size and kind of animal, its
condition (laying hen vs broilers, or milking cow vs a steer), the environ-
mental temperature and the feed conversion and water consumption of the animal,
On the basis of these parameters, the quantity and composition of manure can
be estimated theoretically." It is interesting to note that chemical com-
ponents, although utilized metabol ical ly , are almost all recovered in the
animal excreta. Unused protein in the feces and protein in wasted feed due
to spillage are also present to a significant degree in the waste load.
Studies using litter and manure ' as components in animal feeds
or nutrients for fish ponds show interesting possibilities. These studies
on animal waste utilization were presented at the 1966 National Symposium
on Animal Waste Management at Michigan State University.
Present disposal techniques for animal manures are becoming undesireable.
Farmers no longer use this material as a fertilizer as a matter of course
since the advent of the cheap chemical fertilizers. The fly and odor pro-
blems associated with collecting this material along with the ever increasing
encroachment of suburban areas and the resulting complaints leaves manure
management as the number one headache for 1 ivestock producers.
The system proposed here can be designed to deal effectively with two
major problems of our society: (1) organic solid wastes generated by urban
populations and (2) manure wastes generated in livestock operations.
System Components and Considerations:
Figure A-l is a "black box" representation of a typical "city farm"
system. No attempt has been made here to quantify any of the inputs to
or effluents from the various components of the system. This represents
a totally new technical and economic study and is beyond the scope of this
report.
Comments on each component and operation are offered for clarity and
are not meant to be limiting on the system. Persons skilled in the indivi-
dual technologies involved would, no doubt, have more specific and worthwhile
comments to add.
165
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(Candida Uti1 is)
Waste Water
Grain
Values
-------
Block 1
Operations in block 1 are essentially related with refuse collection
and transfer to the utilization plant site.
Inputs include all types of solid domestic and light commercial (rest-
aurants, offices, etc.) nonmanufacturing wastes. Typical wastes include
bottles, cans, garbage, paper and plastics refuse. Leaf and garden wastes
are discretionary commodities and may or may not be included in design
consideration. Bulky wastes such as automobiles, tree branches, etc
would not be included in this group.
Outputs include segregated organic rubbish including plastic wrapping
materials and aluminum foil, salvage materials such as cans and bottles and
an increased load of dissolved and suspended solids resulting in considerably
higher BOD loadings in the liquid feed to the sewage treatment facility.
Operations:
1. Placement of rubbish in residential collection chute
2. Pneumatic transfer to neighborhood collection site
3. Sorting of waste into salvage and organic refuse components
*t. Disposal of salvageable components to secondary materials users. By
surface transport
5. Shredding of organic refuse to trunk sewer transfer
6. Hydraulic transfer to sewage treatment plant - rubbish utilization
plant location
7. Removal of organic refuse from transfer stream by rotating drum
separator
8. Conveyor transfer of refuse to Block 11 operations
Comments;
Costs for waste water treatment and refuse disposal were summarized
by McKee. The magnitude of the annual per capita costs in each case is
similar. However, the cost distribution is markedly different. In the
case of wastewater treatment approximately seventy one percent of the cost
is amortization of plant and equipment. Refuse disposal shows eighty five
percent of the costs as operating expenses, largely collection costs. With
this cost distribution, and wastewater treatment facilities a must, economies
in refuse collection should be possible in a combined system. Although
municipal financing problems would increase, the convenience of a pneumatic
local collection system with a reduction in fly and odor breeding problems
may show substantial support and approval on the part of the populace
served.
167
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The pneumatic rubbish transfer system has been tested successfully in
}k
Sweden. Sorting of waste for salvage values may, with favorable markets,
be self sustaining. Transfer of organic refuse shredded to the sewer has
been successfully demonstrated in California. Particle sizes for this
test were in the three to four inch dimensional range. Successful contin-
1U9
uous rotary drum separators have been developed and can be applied here.
No untried technologies are proposed. The application considera-
tions to this point are largely economic.
Block 11
Operations in block 11 are concerned with the conversion of organic
rubbish in a two stage process to edible protein in the form of yeast. The
basic technologies of the two processes, hydrolysis and fermentation, are
discussed in the body of this report.
Inputs to the system include:
For hydrolysis; cellulosic raw material in the form of organic refuse,
heat and electrical energy, sulfuric acid, limestone, and process water.
For fermentation; fermentable sugars from hydrolysis process, nutrient
sources including ammonia, potassium, and phosphorous compounds, oxygen
source, electrical energy, cooling media, and process water.
Outputs of the system include:
For hydrolysis; hexose and pentose sugars in solution, lignin, calcium
sulfate, waste steam, organic by products such as furfural, methyl furfural,
etc., and residual sludges.
For fermentation; Candida utilis yeast, residual sugars and nutrients
in waste water stream for use in the hydrolysis plant.
Operat ions;
1. Reduction of organic refuse to fiber state in hydrapulpers
2. Continuous hydrolysis in screw press reactors
3. Neutralization of sugar solution
k. Removal of calcium sulfate sludge from sugar solution
5. Fermentation of sugars
6. Concentration of yeast cells
7. Drying and packaging of yeast
8. Shipment to feed compounding
Comments:
The economic feasibility study of this waste utilization approach
indicates a possible value even under conditions of todays market when
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utilizing mixed organic wastes on a dumping fee or assessment basis. Research
on process and equipment development is required and will probably show areas
for reducing costs as presently estimated.
Block 111
Operations in block 111 are entirely associated with animal production
and by-product industries. Innovations and conveniences in feeding, hygiene
and handling are points of major consideration.
Inputs
Feed compounding; yeast protein and vitamins from fermentation plant,
animal and fish meal protein from animal waste processing plant, recycled
manure from growing area, grain components, lignin from hydrolysis plant,
ftQ Qft 1 *? 9 1^^ 1 Ii"7 1 /iQ
grain additives for other growth factor considerations. ' '
Animal growing units; compounded feeds, water, litter, and environmental
controls.
Abattoir; livestock, poultry, water, chilling or freezing media and
packaging materials.
Animal wastes Processing Plant; bones, eviscera, blood and feathers
from abattoir, dead animals from growing units, process water, and fish
from waste treatment plant.
Outputs:
Feed compounding; controlled special purpose feeds for various animal
23
growing and manure waste control functions.
Animal growing units; eggs, milk, healthy stock to abattoir, dead
stock to animal waste processing plant, manure, and waste water.
Abattoir; meat and poultry, hides, bristle, etc., processing wastes
to animal waste processing plant, waste water.
Animal wastes processing plant; animal and fish meal to feed com-
pounding, gelatin, glue, animal fats and oils, etc., waste water.
Operations:
1. Dry milling and blending of feeds
2. Various breeding, hatching and growing stages providing optimum
environmental and hygienic conditions
3. Preparation and marketing of eggs, milk, etc.
k. Slaughter house
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5. Meatpacking and marketing
6. By product preparation and marketing
7. Animal and fish meal production
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8. Glue and gelatin manufacture and marketing
9. Animal fat and oil manufacture and marketing
Comments:
The operations inputs, and outputs noted above are over simplified
examples of possibilities in block 111 activities. Raw materials for feed
that include items such as manure require considerable genetic research.
The selection of animals for the growing units will probably tend more to
poultry and swine rather than ruminants due to space and feed considera-
tions. The animal waste processing operations are discretionary, controlled
by local economics and markets. In some cases end products may be produced,
whereas, in other instances chemical intermediates may be the more desireable
products.
The design and operation of an environmentally controlled, nutritionally
controlled flock or litter with predicted yields and waste effluents represents
a significant challenge to the animal protein industry and one that would
hopefully yield satisfying technical and economic results.
Block IV
Operations in block IV are the final and perhaps most important overall
steps in the system. This is true at least from the consideration of main-
taining and improving the terrestrial, atmospheric and aquatic environments
in which we live. Treatment of the residual solid wastes produced in the
"City Farm" complex plus the amelioration of the various liquid streams
emanating from the processing plants and the community require advanced
design and planning if the waters are to be made available for in plant
reuse and acceptable for dumping into recreational waters.
Inputs:
Community sewage, hydrolysis plant water, fermentation plant effluent,
animal and poultry manure, abattoir wastes, animal waste processing plant
wastes, electrical energy, oxygen.
Outputs:
Dried sludge, methane, carbon dioxide, ammonia, phosphate and potassium
values, partially purified water suitable for cooling operations or recycling
as waste carriers, purified water for process waters or animal drinking
water, scavenger fish.
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Operations:
1. Settling
2. Sludge digestion
3. Activated sludge plant
k. Trickling filters
5. Clarifiers
6. Tertiary treatment of effluents for process reuse
7. Chlorination
8. Wet Oxidation (Zimmerman process for sludge oxidation)
9. Sludge drying
10. Sludge disposal
11. Fish growing units for sewage consumption
Comments;
The operations noted above are discretionary and utili?ation of one
process in favor of another is a technical-economic optimiration problem.
The utilisation of sewage for fish production requires the maintenance
I \k
of a fixed minimum level of dissolved oxygen in the growinq pond. Perhaps
fish growth can be accomplished in activated sludge units. Oxygen levels
may be maintained by current methods of pumping air through spargers or
perhaps by other techniques such as direct feeding with liquid oxygen,
electrolysis, or membrane transfer techniques. In any event this final
utilization of the wastes available to produce a useful commodity is the
type of approach that must be present in planning waste utilisation systems
of the future.
General Comments:
Considering the most efficient animal protein producer, the hen
(See Figure 18), as a basis for discussion the following general observa-
tions can be made:
1. The amount of feed protein required to produce the U.S. per cap'ta
animal protein availability of 65 grams per day (Table XXXVIII)
is 273 grams.
2. The equivalent amount of feed yeast (50 percent protein) required
to provide this protein requirement is 5^6 grams.
3. The per capita yeast production available from waste loads of k.S
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pounds per capita per day consisting of ^6.6 percent cellulosic
base organic matter is 186 grams via acid hydrolysis-fermentation
processing.
k. The maximum feed protein fraction available from yeast is therefore
3^ percent,
89
5. Poultry feeding studies summari?ed by Bressani indicated that
100 percent of the protein requirement can be supplied from yeast
without harmful effects.
6. The total quantity of yeast protein produced in a "City Farm"
operation is technically consumable by the animal population.
When considering other poultry or animal species the 3^ percent feed
protein fraction supplied by yeast shrinks to the following values:
Broilers - 25.8%
Hogs - 17.9%
Beef Cattle - 7. 15%
It is important to note that additional high grade protein meal is
available within the "City Farm" complex from animal wastes and possibly
fish.
Advantages of the "City Farm" System
I. A current liability, organic refuse, is used to produce a useful
and desireable end product, animal protein.
a) Eliminates associated land and air pollution problems, fly
and vermin breeding sites and the attendant reductions in
property values presently experienced with "dump" disposal
systems.
b) By employing advanced collection techniques rapid disposal
of putrescible materials should enhance health, reduce fly
breeding sites, provide increased convenience to the populace
and reduce costs associated with solid waste collection.
2. Contiguous operations for feed blending, animal growing, meat
preparation and waste utilization reduce shipping problems,
maximize material and technical personnel utilisation and pro-
vides local total process control.
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a) The market for consumer products produced is the surrounding
city. Refrigerated shipments and attendant spoilage should
be largely eliminated.
3. Association of the animal growing units, meat processing and
chemical plant operations with the municipal sewage treatment
plant provides technical competence in waste disposal and max-
imizes reuse of the treated water.
a) Environmental pollution is minimized and controlled.
b) Water of "engineered purity" can be delivered for various
uses reducing overall treatment costs.
The Challenge
The "City Farm" concept is one approach to the tremendous problem
facing this nation and eventually the world to make use of the ever increas-
ing waste of resources. The eventual solutions to the problem of municipal
waste utilization may attempt to solve other problems existing such as those
of food production and animal waste handling approached here.
The challenge to science and engineering today is the economic utiliza-
tion of our myriad wastes.
* U. S. GOVEHNMENT PHtNTING OFFICE : 1969 347-1(10/18 1 73
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ftivlronaental Protection Agency
Library, Region V
1 North lacker Drive
Chicago, Illinois 60606
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